Filed Pursuant to Rule 424(b)(5)
Registration No. 333-237319

PROSPECTUS SUPPLEMENT

(To Prospectus dated May 8, 2020)

Up to $60,000,000

Common Stock

This sales agreement prospectus relates to the issuance and sale of shares of our common stock having an aggregate offering price of up to $60.0 million from time to time through our sales agents, Cantor Fitzgerald & Co., H.C. Wainwright & Co., LLC and B. Riley Securities, Inc. (collectively, the “Sales Agents”). These sales, if any, will be made pursuant to the terms of the Controlled Equity Offering^SM Sales Agreement, or the Sales Agreement, among us and the Sales Agents, dated April 5, 2019, which is filed with the Securities and Exchange Commission (the “SEC”) as an exhibit to the registration statement of which this prospectus supplement is part.

Our common stock is traded on the Nasdaq Global Select Market (the “Nasdaq”), under the symbol “SPPI.” On November 2, 2020, the closing sale price of our common stock on the Nasdaq was $3.49 per share.

Sales of shares of our common stock under this prospectus supplement, if any, may be made by any method deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended, or the Securities Act. The Sales Agents are not required to sell any specific number or dollar amount of shares of our common stock. Each of the Sales Agents has agreed to use its commercially reasonable efforts to sell on our behalf all of the shares of common stock requested to be sold by us, consistent with its normal trading and sales practices, on mutually agreed terms among the Sales Agents and us. There is no arrangement for funds to be received in any escrow, trust or similar arrangement.

The Sales Agents will be entitled to compensation under the terms of the Sales Agreement at a commission rate of up to 3.0% of the gross sales price per share sold. The net proceeds from any sales under this prospectus supplement will be used as described under “Use of Proceeds.” The proceeds we receive from sales of our common stock, if any, will depend on the number of shares actually sold and the offering price of such shares.

In connection with the sale of common stock on our behalf, each of the Sales Agents will be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation of the Sales Agents will be deemed to be underwriting commissions or discounts. We have agreed to provide indemnification and contribution to the Sales Agents with respect to certain liabilities, including liabilities under the Securities Act.

Investing in our common stock involves a high degree of risk. You should review carefully and consider the risks and uncertainties referenced under the heading “Risk Factors” beginning on page S-8 of this prospectus supplement and the risk factors contained in other documents incorporated by reference in this prospectus supplement.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

Cantor H.C. Wainwright & Co. B. Riley Securities

The date of this prospectus supplement is November 6, 2020.

TABLE OF CONTENTS

	Page
EXPLANATORY NOTE		S-1
ABOUT THIS PROSPECTUS		S-1
PROSPECTUS SUMMARY		S-3
THE OFFERING		S-6
RISK FACTORS		S-8
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS		S-10
USE OF PROCEEDS		S-12
DILUTION		S-13
PLAN OF DISTRIBUTION		S-14
LEGAL MATTERS		S-15
EXPERTS		S-15
WHERE YOU CAN FIND MORE INFORMATION		S-15
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE		S-16

TABLE OF CONTENTS

	Page
ABOUT THIS PROSPECTUS		1
PROSPECTUS SUMMARY		2
RISK FACTORS		4
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS		4
USE OF PROCEEDS		6
DESCRIPTIONS OF CAPITAL STOCK WE MAY OFFER		7
DESCRIPTION OF DEBT SECURITIES WE MAY OFFER		11
DESCRIPTION OF WARRANTS WE MAY OFFER		19
DESCRIPTION OF UNITS WE MAY OFFER		22
PLAN OF DISTRIBUTION		24
LEGAL MATTERS		27
EXPERTS		27
WHERE YOU CAN FIND MORE INFORMATION		27
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE		28

EXPLANATORY NOTE

We filed a shelf registration statement on Form S-3 on March 20, 2020, as amended, which was declared effective by the SEC on May 8, 2020 (the “Registration Statement”). The Registration Statement contained a base prospectus covering the offering, issuance and sale by us of securities in an aggregate initial offering price not to exceed $150.0 million, as well as a sales agreement prospectus covering the offering, issuance and sale by us of up to a maximum aggregate offering price of $75.0 million of our common stock pursuant to the terms of the Controlled Equity Offering^SM Sales Agreement, dated April 5, 2019, among us and the Sales Agents (which amount was included in the $150.0 million aggregate offering price set forth in the base prospectus) in an at-the-market offering (the “May 2020 ATM Offering”). On July 29, 2020, we filed a Form 8-K with the SEC terminating the May 2020 ATM Offering. Between May 8, 2020 (the commencement date of the May 2020 ATM Offering) and July 29, 2020, we sold an aggregate of 3,950,398 shares of common stock, for gross proceeds of approximately $15.2 million, pursuant to the May 2020 ATM Offering. On July 29, 2020, the Company entered into an underwriting agreement (the “Underwriting Agreement”), with Jefferies LLC, as representative of the several underwriters listed on Schedule A thereto (the “Underwriters”), relating to an underwritten public offering (the “Equity Offering”) of 21,666,667 shares of the Company’s common stock, at an offering price of $3.00 per share. In addition, the Underwriting Agreement provided the Underwriters with a 30-day option to purchase up to an additional 3,250,000 shares of common stock (the “Underwriters’ Option”). The Underwriters subsequently exercised the Underwriters’ Option and the total gross proceeds to us were approximately $74.8 million. The registration fees associated with the remaining approximately $60.0 million in shares of our common stock that remained unsold following the Equity Offering and the termination of the May 2020 ATM Offering will be utilized in this offering.

ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement and the accompanying prospectus are part of a registration statement on Form S-3 that we filed with the SEC, utilizing a “shelf” registration process. Under the shelf registration process, we may offer shares of our common stock having an aggregate offering price of up to $60.0 million under this prospectus supplement at prices and on terms to be determined by market conditions at the time of offering. This document is in two parts. The first part is this prospectus supplement, including the documents incorporated by reference, which describes the specific terms of this offering. The second part, the accompanying prospectus, including the documents incorporated by reference, provides more general information. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. We urge you to carefully read this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein, before buying any of the securities being offered under this prospectus supplement. This prospectus supplement may add to or update information contained in the accompanying prospectus and the documents incorporated by reference therein. To the extent that any statement we make in this prospectus supplement is inconsistent with statements made in the accompanying prospectus or any documents incorporated by reference therein that were filed before the date of this prospectus supplement, the statements made in this prospectus supplement will be deemed to modify or supersede those made in the accompanying prospectus and such documents incorporated by reference therein.

We further note that the representations, warranties and covenants made by us in any agreement, including the Sales Agreement, that is filed as an exhibit to any document that is incorporated by reference herein were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreement, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

You should rely only on the information contained in this prospectus supplement and the accompanying prospectus, or incorporated by reference herein or therein. We have not, and the Sales

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Agents have not, authorized anyone to provide you with information that is in addition to or different from that contained or incorporated by reference into this prospectus supplement.

We and each of the Sales Agents take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. Neither we nor any of the Sales Agents are offering to sell these securities in any jurisdiction where the offer or sale is not permitted. You should not assume that the information contained or incorporated by reference in this prospectus supplement is accurate as of any date other than as of the date of this prospectus supplement, or in the case of the documents incorporated by reference, the date of such documents, regardless of the time of delivery of this prospectus supplement or any sale of our common stock. Our business, financial condition, liquidity, results of operations and prospects may have changed since those dates. You should read this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein and any free writing prospectus that we may authorize for use in connection with this offering, in their entirety before making an investment decision. You should also read and consider the information in the documents to which we have referred you in the sections of this prospectus supplement titled “Where You Can Find More Information” and “Incorporation of Certain Documents by Reference.”

Unless otherwise indicated or the context otherwise requires, the terms “Company,” “Spectrum Pharmaceuticals,” “we,” “us” and “our” refer to Spectrum Pharmaceuticals, Inc., a Delaware corporation, and its predecessors and consolidated subsidiaries.

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PROSPECTUS SUMMARY

The following is a summary of selected information contained elsewhere in this prospectus supplement or incorporated by reference into this prospectus supplement. It does not contain all of the information that you should consider before buying our securities. You should read this summary together with the entire prospectus supplement and the accompanying prospectus, including our consolidated financial statements, the notes to those consolidated financial statements, our Annual Report on Form 10-K for the fiscal year ended December 31, 2019, and the other documents that are incorporated by reference in this prospectus supplement and the accompanying prospectus, before deciding to buy shares of our common stock. See “Risk Factors” beginning on page S-8 of this prospectus supplement for a discussion of the risks involved in investing in our securities.

Business Overview of Spectrum Pharmaceuticals, Inc.

We are a biopharma company, with a primary strategy comprised of acquiring, developing, and commercializing novel and targeted oncology therapies. Our in-house development organization includes clinical development, regulatory, quality and data management. We continue to build out our commercial and marketing capabilities in the second half of 2020 to prepare for the launch of ROLONTIS.

We have three drugs in development:

• ROLONTIS, a novel long-acting granulocyte colony-stimulating factor (“G-CSF”) for chemotherapy-induced neutropenia, which is under review by the U.S. Food and Drug Administration (the “FDA”). On October 26, 2020, the Company announced that the FDA had deferred action on the Biologics License Application (“BLA”) for ROLONTIS due to the inability to conduct an inspection of our third-party manufacturing facility in South Korea as a result of COVID-19 related travel restrictions;

• Poziotinib, a novel irreversible tyrosine kinase inhibitor under investigation for non-small cell lung cancer (“NSCLC”) tumors with various mutations; and

• Anti-CD20-IFNα, an antibody-interferon fusion molecule directed against CD20 that is in Phase 1 development for treating relapsed or refractory non-Hodgkin’s lymphoma patients (including diffuse large B-cell lymphoma).

Our business strategy is the development of our late-stage assets through commercialization and the sourcing of additional assets that are synergistic with our existing portfolio (through purchase acquisitions, in-licensing transactions, or co-development and marketing arrangements).

Recent Highlights of Our Business, Product Development Initiatives, and Regulatory Approvals

During the nine months ended September 30, 2020, we continued our strategic shift in our business following the completion of the sale of our legacy commercialized drug portfolio in March 2019. We also continued to make meaningful progress in the advancement of our product pipeline, as summarized below:

ROLONTIS, a novel long-acting G-CSF:

We submitted our updated BLA for ROLONTIS with the FDA on October 24, 2019, which was accepted for review by the FDA on December 20, 2019. Our BLA is supported by data from two identically designed Phase 3 clinical trials, ADVANCE and RECOVER, which evaluated the safety and efficacy of ROLONTIS in 643 early-stage breast cancer patients for the treatment of neutropenia due to myelosuppressive chemotherapy. The Prescription Drug User Fee Act date for ROLONTIS was October 24, 2020. Due to the restrictions on travel related to the COVID-19 pandemic, the FDA was unable to conduct an inspection of our third-party

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manufacturing plant in South Korea during the current review cycle. As a result, the FDA deferred action on the application until an inspection can be completed. We will continue to actively work to obtain an approval for ROLONTIS as soon as possible. We have confirmed with the FDA that the deferral is not a Complete Response Letter.

Spectrum presented preclinical data evaluating the administration of ROLONTIS on the same day as chemotherapy at the American Association for Cancer Research (“AACR”) Virtual Annual Meeting II. The duration of neutropenia in a rat model of chemotherapy induced neutropenia was observed to be significantly shorter with eflapegrastim versus pegfilgrastim, regardless of the timing of administration: concomitantly or on the same day post-chemotherapy at 2, 5 or 24 hours post-chemotherapy.

A company sponsored clinical study has been initiated to evaluate the administration of ROLONTIS on the same day as chemotherapy. The first patient was dosed in April 2020. The trial will evaluate the duration of severe neutropenia when administered at three different time points on the same day following standard chemotherapy in patients with early stage breast cancer.

Poziotinib, an irreversible tyrosine kinase inhibitor targeting EGFR and HER2 mutations:

In October 2017, we announced the start of a pivotal Phase 2 global study with active sites in the U.S., Canada and Europe (“ZENITH20”). The ZENITH20 study consists of seven cohorts of NSCLC patients. Cohorts 1 (EGFR) and 2 (HER2) have completed enrollment of previously treated NSCLC patients with exon 20 mutations. Cohort 3 (EGFR) recently completed enrollment and Cohort 4 (HER2) is currently enrolling first-line NSCLC patients with exon 20 mutations. Cohorts 1-4 are each independently powered for a pre-specified statistical hypothesis and the primary endpoint is objective response rate (“ORR”). Cohort 5 includes previously treated or treatment-naïve NSCLC patients with EGFR or HER2 exon 20 insertion mutations. Cohort 6 includes NSCLC patients with classical EGFR mutations who progressed while on treatment with first-line osimertinib and developed an additional EGFR mutation. Cohort 7 includes NSCLC patients with a variety of less common mutations in EGFR or HER2 exons 18-21 or the extracellular or transmembrane domains.

On December 26, 2019, we announced that the pre-specified primary endpoint in our Phase 2 clinical trial evaluating poziotinib in previously treated NSCLC patients with EGFR exon 20 insertion mutations was not met in Cohort 1 of the ZENITH20 trial. Cohort 1 enrolled a total of 115 patients who received 16 mg/day of poziotinib. The intent-to-treat analysis showed that 17 patients had a response (by RECIST) and 62 patients had stable disease for a 68.7% disease control rate (“DCR”). The confirmed ORR was 14.8% (95% Confidence Interval (“CI”) 8.9%-22.6%). Based on the FDA reviewed protocol, an observed ORR of 30%, with 17% as the lower bound for 95% CI was considered to be the clinically meaningful efficacy in our study. The median duration of response was 7.4 months and progression free survival was 4.2 months. The safety profile was in-line with the type of adverse events seen with other second-generation EGFR tyrosine kinase inhibitors.

We presented additional results for Cohort 1 from our Phase 2 clinical trial, ZENITH20, evaluating poziotinib in previously treated NSCLC patients with EGFR exon 20 insertion mutations, at a plenary session of the AACR Annual Meeting on April 27, 2020. The podium presentation included additional safety and efficacy data. We also provided an update on our strategy for the ZENITH20 Phase 2 clinical trial evaluating poziotinib in NSCLC patients with EGFR and HER2 exon 20 insertion mutations. The protocol has been amended to explore additional dosing regimens and the earlier use of corticosteroids in an effort to increase drug compliance.

On July 27, 2020, we announced that we met the pre-specified primary endpoint for Cohort 2 in the ZENITH20 Phase 2 clinical trial evaluating previously treated NSCLC patients with HER2 exon 20 insertion mutations. Cohort 2 of the ZENITH20 clinical trial enrolled a total of 90 patients who received an oral, once daily dose of 16 mg of poziotinib. All the patients had failed at least one line of prior systemic therapy with 60

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patients (67%) having failed two or more prior therapies, including chemotherapy and immunotherapy. All responses were read independently and confirmed by a central imaging laboratory using RECIST criteria. The intent-to-treat analysis demonstrated a confirmed ORR of 27.8% (95% CI of 18.9%-38.2%). Based on the pre-specified statistical hypothesis for the primary endpoint, the observed lower bound of 18.9% exceeded the pre-specified lower bound of 17% in this heavily pre-treated population. The safety profile was in-line with the type of adverse events seen with other second-generation EGFR tyrosine kinase inhibitors. We have been granted a pre-NDA meeting with the FDA based on the positive results from Cohort 2 to seek a path forward for poziotinib registration for the treatment of patients with previously treated locally advanced or metastatic NSCLC with HER2 exon 20 insertion mutations.

In September 2020, we presented the results from Cohort 2 at the European Society for Medical Oncology (ESMO) Virtual Congress.

We expect to provide a dosing strategy update and topline results from Cohort 3 of the ZENITH20 trial in first-line EGFR NSCLC patients by year end 2020.

You can find more information about us in our filings with the SEC referenced in the sections in this document titled “Where You Can Find More Information” and “Incorporation of Certain Documents by Reference.”

Corporate Information

Spectrum Pharmaceuticals, Inc. is a Delaware corporation that was originally incorporated in Colorado as Americus Funding Corporation in December 1987, became NeoTherapeutics, Inc. in August 1996, was reincorporated in Delaware in June 1997, and was renamed Spectrum Pharmaceuticals, Inc. in December 2002. More comprehensive information about our products and us is available through our website at www.sppirx.com. The information on our website is not incorporated by reference into this prospectus supplement. Our principal executive offices are located at 11500 South Eastern Avenue, Suite 240, Henderson, Nevada 89052, and our telephone number is (702) 835-6300.

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THE OFFERING

The following summary contains basic information about our common stock and the offering and is not intended to be complete. It does not contain all of the information that may be important to you. For a more complete understanding of our common stock, you should read the section titled “Description of Capital Stock we may Offer.”

Issuer	Spectrum Pharmaceuticals, Inc.
Common stock offered	Shares of our common stock having an aggregate offering price of up to $60.0 million.
Common stock to be outstanding after this offering(1)	Up to 163,123,149 shares, assuming a sales price of $3.49 per share, which was the closing price of our common stock on the Nasdaq on November 2, 2020. The actual number of shares issued will vary depending on the sales price under this offering.
Plan of Distribution	“At the market offering” that may be made from time to time through our Sales Agents. See “Plan of Distribution” beginning on page S-14 of this prospectus supplement.
Use of Proceeds	We intend to use the net proceeds from this offering, if any, for general corporate purposes, including, without limitation, research and development and clinical development costs to support the advancement of our in-development drug candidates, activities in connection with the launch of our in-development drug candidates, including hiring and building inventory supply, making acquisitions of assets, businesses, companies or securities, capital expenditures and for working capital. See “Use of Proceeds” beginning on page S-12 of this prospectus supplement.
Risk Factors	Investment in our common stock involves substantial risks. You should read carefully the “Risk Factors” beginning on page S-8 of this prospectus supplement and in documents incorporated by reference into this prospectus supplement, including the risk factors incorporated by reference from our filings with the SEC.
Nasdaq symbol	SPPI

⁽¹⁾  The common stock outstanding after the offering is based on 145,931,172 shares of our common stock outstanding as of September 30, 2020 and the sale of 17,191,977 shares of our common stock at an assumed offering price of $3.49 per share, the last reported sale price of our common stock on the Nasdaq on November 2, 2020 and excludes the following:

• 7,742,138 shares of our common stock issuable upon the exercise of options outstanding as of September 30, 2020, having a weighted average exercise price of $7.80 per share;

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• 511,724 shares of our common stock issuable upon the vesting and settlement of outstanding restricted stock units, outstanding as of September 30, 2020, having a weighted average grant date fair value of $25.24 per share; and

• an aggregate of 16,806,015 shares of our common stock reserved for future issuance as of September 30, 2020, under our 2018 Long-Term Incentive Plan and 2009 Employee Stock Purchase Plan.

Unless otherwise indicated, all information in this prospectus supplement assumes no exercise of the outstanding options or settlement of the restricted stock units described above.

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RISK FACTORS

Investment in our securities involves risks. Prior to making a decision about investing in our securities, you should consider carefully all of the information included in and incorporated by reference or deemed to be incorporated by reference into this prospectus supplement, including the risk factors incorporated by reference herein from our Annual Report on Form 10-K for the year ended December 31, 2019, filed with the SEC on March 2, 2020, as updated by annual, quarterly and other reports and documents we file with the SEC after the date of this prospectus supplement and that are incorporated by reference herein or in any free writing prospectus. Each of these risk factors could have a material adverse effect on our business, results of operations, financial position or cash flows, which may result in the loss of all or part of your investment. The risks and uncertainties we have described are not the only ones we face. Additional risks and uncertainties not presently known to us or that we currently consider immaterial may also impair our business operations. If any of these risks actually occur, our business and financial results could be harmed. In that case, the trading price of our common stock or other securities could decline. Please also read carefully the section below titled “Cautionary Note Regarding Forward-Looking Statements.”

Risks Related to This Offering

Our management will have broad discretion as to the use of the proceeds from this offering and may not use the proceeds effectively.

Because we have not designated the amount of net proceeds from this offering to be used for any particular purpose, our management will have broad discretion as to the application of the net proceeds from this offering and could use them for purposes other than those contemplated at the time of the offering. Our management may use the net proceeds for corporate purposes that may not improve our financial condition or market value.

Future sales of substantial amounts of our common stock, or the possibility that such sales could occur, could adversely affect the market price of our common stock.

We may issue up to $60.0 million of common stock from time to time in this offering. The issuance from time to time of shares in this offering, as well as our ability to issue such shares in this offering, could have the effect of depressing the market price or increasing the market price volatility of our common stock. See “Plan of Distribution” on page S-14 of this prospectus supplement for more information about the possible adverse effects of our sales under the Sales Agreement.

You may experience immediate and substantial dilution.

The offering price per share in this offering may exceed the net tangible book value per share of our common stock. Assuming that an aggregate of 17,191,977 shares of our common stock are sold at a price of $3.49 per share pursuant to this prospectus supplement which was the last reported sale price of our common stock on the Nasdaq on November 2, 2020, for aggregate net proceeds of approximately $58.2 million, after deducting commissions and estimated aggregate offering expenses payable by us, you would experience immediate dilution of $2.12 per share, representing a difference between our as adjusted net tangible book value per share as of September 30, 2020, after giving effect to this offering and the assumed offering price. To the extent that any options or warrants are exercised, any restricted stock units vest and are settled, any new equity awards are issued under our equity incentive plans, or we otherwise issue additional shares of common stock in the future (including shares issued in connection with strategic and other transactions), you will experience further dilution. In addition, we may choose to raise additional capital due to market conditions or strategic considerations, even if we believe we have sufficient funds for our current or future operating plans. To the extent that additional capital is raised through the sale of equity or convertible debt securities, the issuance of these securities could result in further dilution to our stockholders. See the section entitled “Dilution” on page S-13 of this prospectus supplement for a more detailed illustration of the dilution you would incur if you participate in this offering.

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You may experience future dilution as a result of future equity offerings.

In order to raise additional capital, we may in the future offer additional shares of our common stock or other securities convertible into or exchangeable for our common stock. We cannot assure you that we will be able to sell shares or other securities in any other offering at a price per share that is equal to or greater than the price per share paid by investors in this offering, and investors purchasing shares or other securities in the future could have rights superior to existing stockholders. The price per share at which we sell additional shares of our common stock or other securities convertible into or exchangeable for our common stock in future transactions may be higher or lower than the price per share in this offering. As of September 30, 2020, approximately 25,059,877 shares of common stock that are either subject to outstanding options, issuable upon vesting of outstanding restricted stock awards or restricted stock units, or reserved for future issuance under our equity incentive plans (including our employee stock purchase plan) are eligible for sale in the public market to the extent permitted by the provisions of various vesting schedules and Rule 144 and Rule 701 under the Securities Act.

It is not possible to predict the actual number of shares we will sell under the Sales Agreement, or the gross proceeds resulting from those sales.

Subject to certain limitations in the Sales Agreement and compliance with applicable laws, we have the discretion to deliver a placement notice to the Sales Agents at any time throughout the term of the Sales Agreement. The number of shares that are sold through the Sales Agents after delivering a placement notice will fluctuate based on a number of factors, including the market price of our common stock during the term of the Sales Agreement, the limits we set with the Sales Agents in any applicable placement notice, and the demand for our common stock during the term of the Sales Agreement. Because the price per share of each share sold will fluctuate during the term of the Sales Agreement, it is not currently possible to predict the number of shares that will be sold or the gross proceeds to be raised in connection with the sales of shares of common stock offered under this prospectus supplement.

The common stock offered hereby will be sold in “at the market offerings,” and investors who buy shares at different times will likely pay different prices.

Investors who purchase shares in this offering at different times will likely pay different prices, and so may experience different levels of dilution and different outcomes in their investment results. We will have discretion, subject to market demand, to vary the timing, prices and numbers of shares sold in this offering. Investors may experience a decline in the value of the shares they purchase in this offering as a result of sales made at prices lower than the prices they paid.

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein contain certain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), in reliance upon the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Forward-looking statements include, without limitation, statements regarding our future product development and commercialization activities and costs, the revenue potential (licensing, royalty and sales) of our products and product candidates, the impact of the COVID-19 global pandemic on our business, the success, safety and efficacy of our drug products, revenues, development and commercialization timelines, product acquisitions, accounting principles, litigation expenses, liquidity and capital resources and trends and other statements containing forward-looking words, such as, “believes,” “may,” “could,” “would,” “will,” “expects,” “intends,” “estimates,” “anticipates,” “plans,” “seeks,” “continues,” or the negative thereof or variation thereon or similar terminology (although not all forward-looking statements contain these words). Such forward-looking statements are based on the reasonable beliefs of our management as well as assumptions made by and information currently available to our management. Readers should not put undue reliance on these forward-looking statements. Forward-looking statements are inherently subject to risks and uncertainties, some of which cannot be predicted or quantified; therefore, our actual results may differ materially from those described in any forward-looking statements.

Factors that might cause these differences include, but are not limited to, those described in our periodic reports filed with the SEC, including our Annual Report on Form 10-K for the fiscal year ended December 31, 2019, as well as those discussed elsewhere in this prospectus supplement, and the following factors:

• our ability to successfully develop, obtain regulatory approval, and market our products;

• the approval, or timing of approval, of our products or new indications for our products by the FDA and other international regulatory agencies;

• the overall impact of COVID-19 on our business, including on the timing of the FDA’s completion of its review of our BLA for ROLONTIS;

• actions by the FDA and other regulatory agencies, including international agencies;

• the timing and/or results of pending or future clinical trials, and our reliance on contract research organizations;

• our ability to maintain sufficient cash resources to fund our business operations;

• our history of net losses;

• our ability to enter into strategic alliances with partners for manufacturing, development and commercialization;

• our competitors’ progress with their drug development programs, which could adversely impact the perceived or actual value of our in-development drugs;

• the ability of our manufacturing partners to meet our product demands and timelines;

• our ability to identify and acquire new product candidates and to successfully integrate those product candidates into our operations;

• our ability to protect our intellectual property rights;

• the impact of legislative or regulatory reform on the pricing for pharmaceutical products;

• the impact of any litigation to which we are, or may become a party;

• our ability, and that of our suppliers, development partners, and manufacturing partners, to comply with laws, regulations and standards that govern or affect the pharmaceutical and biotechnology industries; and

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• our ability to maintain the services of our key executives and other personnel.

We urge you to consider these factors carefully in evaluating the forward-looking statements contained in this prospectus supplement. All subsequent written or oral forward-looking statements attributable to our company or persons acting on our behalf are expressly qualified in their entirety by these cautionary statements. The forward-looking statements included in this prospectus supplement are made only as of the date of this prospectus supplement. We undertake no obligation to update publicly any forward-looking statements, whether as a result of new information, future events or otherwise, except to the extent that we are required to do so by law.

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USE OF PROCEEDS

The amount of proceeds from this offering will depend upon the number of shares of our common stock sold and the market price at which they are sold. There can be no assurance that we will be able to sell any shares under or fully utilize the Sales Agreement as a source of financing. Because there is no minimum offering amount required as a condition to close this offering, the actual total proceeds to us, if any, are not determinable at this time.

We intend to use the net proceeds, if any, from this offering for general corporate purposes, including, without limitation, research and development and clinical development costs to support the advancement of our in-development drug candidates, activities in connection with the launch of our in-development drug candidates, including hiring and building inventory supply, making acquisitions of assets, businesses, companies or securities, capital expenditures and for working capital. We have not determined the amount of net proceeds to be used specifically for such purposes. As a result, management will retain broad discretion over the allocation of net proceeds.

The amounts and timing of our actual expenditures will depend on numerous factors, including our development and commercialization efforts, as well as the amount of cash used in our operations. We therefore cannot estimate with certainty the amount of net proceeds to be used for the purposes described above. We may find it necessary or advisable to use the net proceeds for other purposes, and we will have broad discretion in the application of the net proceeds. Pending the uses described above, we plan to invest the net proceeds from this offering in short-term, investment-grade, interest-bearing securities.

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DILUTION

If you invest in our common stock, your ownership interest will be diluted to the extent of the difference between the public offering price per share and the as-adjusted net tangible book value per share after this offering.

The net tangible book value of our common stock on September 30, 2020, was approximately $165.7 million, or $1.14 per share of common stock. We calculate net tangible book value per share by dividing the net tangible book value, which is tangible assets less total liabilities, by the number of outstanding shares of our common stock. Dilution with respect to net tangible book value per share represents the difference between the amount per share paid by purchasers of shares of common stock in this offering and the net tangible book value per share of our common stock immediately after this offering.

After giving effect to the sale of our common stock pursuant to this prospectus supplement in the aggregate amount of $60.0 million at an assumed offering price of $3.49 per share, the last reported sale price of our common stock on the Nasdaq on November 2, 2020, and after deducting commissions, which, for purposes of estimating dilution per share to new investors in this offering, we have assumed to be 3.0% of the gross sales price per share sold, and estimated aggregate offering expenses payable by us, our net tangible book value as of September 30, 2020 would have been approximately $223.8 million, or $1.37 per share of common stock. This represents an immediate increase in the net tangible book value of $0.23 per share to our existing stockholders and an immediate dilution in net tangible book value of $2.12 per share to new investors. The following table illustrates this per share dilution:

Assumed offering price per share			$ 3.49
Net tangible book value per share as of September 30, 2020	$	1.14
Increase in net tangible book value per share after this offering	$	0.23
As-adjusted net tangible book value per share after this offering			$1.37
Dilution per share to new investors in this offering			$2.12

The above discussion and table are based on 145,931,172 shares of our common stock outstanding as of September 30, 2020 and excludes the following:

• 7,742,138 shares of our common stock issuable upon the exercise of options outstanding as of September 30, 2020, having a weighted average exercise price of $7.80 per share;

• 511,724 shares of common stock issuable upon the vesting and settlement of outstanding restricted stock units, outstanding as of September 30, 2020, having a weighted average grant date fair value of $25.24 per share; and

• an aggregate of 16,806,015 shares of our common stock reserved for future issuance as of September 30, 2020 under our 2018 Long-Term Incentive Plan and 2009 Employee Stock Purchase Plan.

To the extent that any of these outstanding options are exercised or restricted stock units are settled, there will be further dilution to new investors.

S-13

PLAN OF DISTRIBUTION

We previously entered into the Sales Agreement with the Sales Agents on April 5, 2019, under which we may offer and sell up to $60.0 million of shares of our common stock from time to time through the Sales Agents, acting as agents. Sales of shares of our common stock, if any, under this prospectus supplement may be made at market prices by any method deemed to be an “at the market” offering as defined in Rule 415(a)(4) under the Securities Act, including, without limitation, sales made directly on the Nasdaq or any other existing trading market for our common stock.

We may instruct the Sales Agents not to sell our common stock if the sales cannot be effected at or above the price designated by us from time to time. We or the Sales Agents may suspend the offering of common stock upon notice and subject to other conditions.

We will pay the Sales Agents commissions, in cash, for their services for acting as a Sales Agent in the sale of our common stock. The Sales Agents will be entitled to compensation at a fixed commission rate of up to 3.0% of the gross sales price per share sold. We have also agreed to reimburse the Sales Agents for certain specified expenses, including the fees and disbursements of their legal counsel, in an amount not to exceed $50,000. We estimate that the total expenses for the offering, excluding compensation and reimbursement payable to the Sales Agents under the terms of the Sales Agreement, will be approximately $130,000. Because there is no minimum offering amount required as a condition to close this offering, the actual total public offering amount, commissions and proceeds to us, if any, are not determinable at this time.

Settlement for sales of our common stock will occur on the second trading day following the date on which any sales are made, or on some other date that is agreed upon by us and the Sales Agents in connection with a particular transaction, in return for payment of the net proceeds to us. Sales of our common stock as contemplated in this prospectus supplement will be settled through the facilities of The Depository Trust Company or by such other means as we and the Sales Agents may agree upon. There is no arrangement for funds to be received in an escrow, trust or similar arrangement.

The Sales Agents will use their commercially reasonable efforts, consistent with their sales and trading practices, to solicit offers to purchase shares of our common stock under the terms and subject to the conditions set forth in the Sales Agreement. In connection with the sale of shares of our common stock on our behalf, each of the Sales Agents may be deemed to be an “underwriter” within the meaning of the Securities Act and the compensation of the Sales Agents may be deemed to be underwriting commissions or discounts. We have agreed to provide indemnification and contribution to the Sales Agents against certain civil liabilities, including liabilities under the Securities Act.

The offering pursuant to the Sales Agreement will terminate upon the termination of the Sales Agreement as permitted therein. We and the Sales Agents may each terminate the Sales Agreement at any time upon ten days’ prior notice.

The Sales Agents and their affiliates may provide various investment banking and other financial services for us and our affiliates, for which services they may in the future receive customary fees. To the extent required by Regulation M, the Sales Agents will not engage in any market making activities involving our common stock while the offering is ongoing under this prospectus supplement.

This summary of the material provisions of the Sales Agreement does not purport to be a complete statement of its terms and conditions. A copy of the Sales Agreement is filed as an exhibit to the Registration Statement of which this prospectus supplement forms a part and is incorporated by reference in this prospectus supplement.

This prospectus supplement in electronic format may be made available on a website maintained by each of the Sales Agents and the Sales Agents may distribute this prospectus supplement electronically.

S-14

LEGAL MATTERS

The validity of the securities being offered hereby will be passed on by Paul Hastings, LLP, San Diego, California. The Sales Agents are being represented in connection with this offering by Cooley LLP, New York, New York.

EXPERTS

The financial statements, and the related financial statement schedule, incorporated in this prospectus supplement by reference from the Company’s Annual Report on Form 10-K, and the effectiveness of Spectrum Pharmaceuticals, Inc.’s internal control over financial reporting have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their reports, which are incorporated herein by reference. Such financial statements and financial statement schedule have been so incorporated in reliance upon the reports of such firm given upon their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and special reports, proxy statements and other information with the SEC. The SEC maintains an Internet website at http://www.sec.gov that contains reports, proxy and information statements, and other information regarding issuers that file electronically with the SEC, including Spectrum Pharmaceuticals, Inc. You may also access our reports and proxy statements free of charge at our Internet website, www.spprix.com. The information contained in, or that can be accessed through, our website is not part of this prospectus supplement. The prospectus included in this filing is part of a registration statement filed by us with the SEC. The full registration statement can be obtained from the SEC, as indicated above, or from us.

S-15

INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

This prospectus supplement is part of a Registration Statement on Form S-3 filed by us with the SEC. This prospectus supplement does not contain all of the information set forth in the Registration Statement, certain parts of which are omitted in accordance with the rules and regulations of the SEC. For further information about us and the securities offered by this prospectus supplement, we refer you to the Registration Statement and its exhibits and schedules which may be obtained as described herein.

The SEC allows us to “incorporate by reference” information into this prospectus supplement. This means that we can disclose important information about us and our financial condition to you by referring you to another document filed separately with the SEC. The information incorporated by reference is considered to be part of this prospectus supplement. This prospectus supplement incorporates by reference the documents listed below that we have previously filed with the SEC:

• Our Annual Report on Form 10-K for the fiscal year ended December 31, 2019, as filed with the SEC on March 2, 2020;

• Our Definitive Proxy Statement on Schedule 14A, as filed with the SEC on April 22, 2020 (to the extent incorporated by reference into Part III of our Annual Report on Form 10-K for the fiscal year ended December 31, 2019);

• Our Quarterly Reports on Form 10-Q for: (i) the three months ended March 31, 2020, as filed with the SEC on May 7, 2020; (ii) the six months ended June  30, 2020, as filed with the SEC on August 10, 2020; and (iii) the nine months ended September  30, 2020, as filed with the SEC on November 4, 2020;

• Our Current Reports on Form 8-K, as filed with the SEC on March 13, 2020, April 23, 2020, June  19, 2020, July 27, 2020, July  29, 2020 and August 3, 2020; and

• The description of our common stock contained in the Registration of Securities of Certain Successor Issuers filed pursuant to Section 12(g) of the Exchange Act on Form 8-B on June 27, 1997, including any amendments or reports filed for the purpose of updating such description.

We also incorporate by reference any future filings (other than information in current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such forms that are related to such items) made with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, until we sell all of the securities offered by this prospectus supplement. Information in such future filings updates and supplements the information provided in this prospectus supplement. Any statements in any such future filings will automatically be deemed to modify and supersede any information in any document we previously filed with the SEC that is incorporated or deemed to be incorporated herein by reference to the extent that statements in the later filed document modify or replace such earlier statements.

Any information in any of the foregoing documents will automatically be deemed to be modified or superseded to the extent that information in this prospectus supplement or the accompanying prospectus or in a later filed document that is incorporated or deemed to be incorporated herein by reference modifies or replaces such information. Any statement so modified or superseded will not be deemed, except as so modified or superseded, to constitute a part of this prospectus supplement.

Upon written or oral request, we will provide to you, without charge, a written copy of any or all of the documents that are incorporated by reference into this prospectus supplement and the accompanying prospectus but not delivered with the prospectus, including exhibits which are specifically incorporated by reference into such documents. Requests should be directed to: Spectrum Pharmaceuticals, Inc., Attention: Investor Relations, 11500 South Eastern Avenue, Suite 240, Henderson, Nevada 89052, telephone (702) 835-6300.

Statements contained in this prospectus supplement as to the contents of any contract or other documents are not necessarily complete, and in each instance investors are referred to the copy of the contract or other document filed as an exhibit to the Registration Statement, each such statement being qualified in all respects by such reference and the exhibits and schedules thereto.

S-16

PROSPECTUS

$150,000,000

Common Stock

Preferred Stock

Debt Securities

Warrants

Units

This prospectus relates to common stock, preferred stock, debt securities, warrants for debt or equity securities and units consisting of the foregoing that we may sell from time to time in one or more transactions. We will provide the specific terms and conditions of these transactions and the securities we may sell in supplements to this prospectus prepared in connection with each transaction. The applicable prospectus supplement will contain information, where applicable, as to other listings, if any, on the Nasdaq Global Select Market, or the NASDAQ, or any securities exchange of the securities covered by the prospectus supplement. Any such prospectus supplement may also add, update or change information in this prospectus. We may also authorize one or more free writing prospectuses to be provided to you in connection with these offerings. You should carefully read this prospectus, any applicable prospectus supplement and any related free writing prospectuses, as well as the documents incorporated by reference or deemed to be incorporated by reference into this prospectus, carefully before you invest. This prospectus may not be used to offer or sell securities unless accompanied by a prospectus supplement.

Our common stock is traded on the NASDAQ under the symbol “SPPI.”

Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties referenced under the heading “Risk Factors” on page 4 of this prospectus and contained in our filings made with the Securities and Exchange Commission and the applicable prospectus supplement.

The securities may be sold directly by us to investors, through agents designated from time to time or to or through underwriters or dealers. For additional information on the methods of sale, you should refer to the section entitled “Plan of Distribution” in this prospectus. If any underwriters are involved in the sale of these securities with respect to which this prospectus is being delivered, the names of such underwriters and any applicable commissions or discounts and over-allotment options will be set forth in a prospectus supplement. The price to the public of such securities and the net proceeds that we expect to receive from such sale will also be set forth in a prospectus supplement. No securities may be sold without delivery of this prospectus and the applicable prospectus supplement describing the method and terms of the offering of such securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is May 8, 2020.

TABLE OF CONTENTS

	Page
ABOUT THIS PROSPECTUS		1
PROSPECTUS SUMMARY		2
RISK FACTORS		4
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS		4
USE OF PROCEEDS		6
DESCRIPTIONS OF CAPITAL STOCK WE MAY OFFER		7
DESCRIPTION OF DEBT SECURITIES WE MAY OFFER		11
DESCRIPTION OF WARRANTS WE MAY OFFER		19
DESCRIPTION OF UNITS WE MAY OFFER		22
PLAN OF DISTRIBUTION		24
LEGAL MATTERS		27
EXPERTS		27
WHERE YOU CAN FIND MORE INFORMATION		27
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE		28

ABOUT THIS PROSPECTUS

This prospectus is part of a shelf registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or the SEC, under the Securities Act of 1933, as amended, or the Securities Act. utilizing a “shelf” registration process. Under this shelf registration process, we may, from time to time, offer and sell any combination of the securities described in this prospectus in one or more offerings for an aggregate offering amount of up to $150,000,000.

This prospectus only provides you with a general description of the securities we may sell in these transactions. Each time we sell any securities under this prospectus, we will provide a prospectus supplement that will contain specific information about the terms of that offering. The prospectus supplement also may add, update or change information contained in this prospectus. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. This prospectus does not contain all of the information included in the Registration Statement we filed with the SEC. For further information about us or the securities offered hereby, you should carefully read this prospectus, any applicable prospectus supplement, any related free writing prospectuses, the information and documents incorporated herein by reference and the additional information under the heading “Where You Can Find More Information” before making an investment decision.

You should rely only on the information contained or incorporated by reference in this prospectus, any applicable prospectus supplement and any related free writing prospectuses that we may authorize to be provided to you. We have not authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. This prospectus and any accompanying supplement to this prospectus are not an offer to sell these securities and are not soliciting an offer to buy these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus, any applicable prospectus supplement or any related free writing prospectuses, as well as information we have previously filed with the SEC and incorporated by reference, is accurate only as of the date on the cover of those documents. If any statement in one of these documents is inconsistent with a statement in another document having a later date-for example, a document incorporated by reference in this prospectus-the statement in the document having the later date modifies or supersedes the earlier statement as our business, financial condition, results of operations and prospects may have changed since the earlier dates.

This prospectus may not be used to consummate sales of any of these securities unless it is accompanied by a prospectus supplement. To the extent there are inconsistencies between any prospectus supplement, this prospectus and/or any documents incorporated by reference, the document with the most recent date will control.

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PROSPECTUS SUMMARY

Unless otherwise indicated or the context otherwise requires, the terms “Company,” “Spectrum Pharmaceuticals,” “we,” “us” and “our” refer to Spectrum Pharmaceuticals, Inc., a Delaware corporation, and its predecessors and consolidated subsidiaries.

Business Overview of Spectrum Pharmaceuticals, Inc.

We are a biopharma company, with a primary strategy comprised of acquiring, developing, and commercializing novel and targeted oncology therapies. Our in-house development organization includes clinical development, regulatory, quality and data management. We plan to build out our commercial and marketing capabilities in the second half of 2020 to prepare for the launch of ROLONTIS.

We have three drugs in development:

• ROLONTIS, a novel long-acting granulocyte colony-stimulating for chemotherapy-induced neutropenia which has been filed with the FDA and has a Prescription Drug User Fee Act date of October 24, 2020;

• Poziotinib, a novel irreversible tyrosine kinase inhibitor under investigation for non-small cell lung cancer tumors with various mutations; and

• Anti-CD20-IFNá, an antibody-interferon fusion molecule directed against CD20 that is in Phase 1 development for treating relapsed or refractory non-Hodgkin’s lymphoma patients (including diffuse large B-cell lymphoma).

Our business strategy is the development of our late-stage assets through commercialization and the sourcing of additional assets that are synergistic with our existing portfolio (through purchase acquisitions, in-licensing transactions, or co-development and marketing arrangements).

On March 1, 2019, we completed the sale of our seven then-commercialized drugs, including FUSILEV, KHAPZORY, FOLOTYN, ZEVALIN, MARQIBO, BELEODAQ, and EVOMELA (the “Commercial Product Portfolio”) to Acrotech Biopharma LLC (“Acrotech”). Upon closing we received $158.8 million in an upfront cash payment of which $4 million was held in escrow until November 5, 2019. We are also entitled to receive up to an aggregate of $140 million upon Acrotech’s future achievement of certain regulatory milestones (totaling $40 million) and sales-based milestones (totaling $100 million) relating to the Commercial Product Portfolio.

Corporate Information

Spectrum Pharmaceuticals, Inc. is a Delaware corporation that was originally incorporated in Colorado as Americus Funding Corporation in December 1987, became NeoTherapeutics, Inc. in August 1996, was reincorporated in Delaware in June 1997, and was renamed Spectrum Pharmaceuticals, Inc. in December 2002. More comprehensive information about our products and us is available through our website at www.sppirx.com. The information on our website is not incorporated by reference into this prospectus. Our principal executive offices are located at 11500 South Eastern Avenue, Suite 240, Henderson, Nevada 89052, and our telephone number is (702) 835-6300.

Securities We May Offer

We may offer shares of our common stock and preferred stock, debt securities, warrants for debt or equity securities and units consisting of the foregoing, from time to time under this prospectus, together with any

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applicable prospectus supplement and related free writing prospectus, at prices and on terms to be determined by market conditions at the time of offering. This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities, including, to the extent applicable:

• designation or classification;

• aggregate principal amount or aggregate offering price;

• maturity, if applicable;

• original issue discount, if any;

• rates and times of payment of interest or dividends, if any;

• redemption, conversion, exchange or sinking fund terms, if any;

• conversion or exchange prices or rates, if any, and, if applicable, any provisions for changes to or adjustments in the conversion or exchange prices or rates and in the securities or other property receivable upon conversion or exchange;

• ranking;

• restrictive covenants, if any;

• voting or other rights, if any; and

• important U.S. federal income tax considerations.

A prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change information contained in this prospectus or in documents we have incorporated by reference. However, no prospectus supplement or free writing prospectus will offer a security that is not registered and described in this prospectus at the time of the effectiveness of the Registration Statement of which this prospectus is a part.

The securities may be offered directly by us or by any selling security holder from time to time, through agents designated by us or to or through underwriters, brokers or dealers. We will provide specific information about any selling security holders in one or more supplements to this prospectus. We, and our underwriters or agents, reserve the right to accept or reject all or part of any proposed purchase of securities. If we do offer securities through underwriters or agents, we will include in the applicable prospectus supplement:

• the names of those underwriters or agents;

• applicable fees, discounts and commissions to be paid to them;

• details regarding options to purchase additional securities, if any; and

• the net proceeds to us.

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RISK FACTORS

Investment in our securities involves risks. Prior to making a decision about investing in our securities, you should consider carefully all of the information included in and incorporated by reference or deemed to be incorporated by reference in this prospectus or the applicable prospectus supplement, including the risk factors incorporated by reference herein from our Annual Report on Form 10-K for the year ended December 31, 2019, filed with the SEC on March 2, 2020, as updated by annual, quarterly and other reports and documents we file with the SEC after the date of this prospectus and that are incorporated by reference herein or in the applicable prospectus supplement or any free writing prospectus. Each of these risk factors could have a material adverse effect on our business, results of operations, financial position or cash flows, which may result in the loss of all or part of your investment. The risks and uncertainties we have described are not the only ones we face. Additional risks and uncertainties not presently known to us or that we currently consider immaterial may also impair our business operations. If any of these risks actually occur, our business and financial results could be harmed. In that case, the trading price of our common stock or other securities could decline. To the extent a particular offering implicates additional known material risks, we will include a discussion of those risks in the applicable prospectus supplement.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and the documents incorporated by reference into this prospectus contain certain forward-looking statements within the meaning of Section 27A of the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act, in reliance upon the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. Forward-looking statements include, without limitation, statements regarding the success, safety and efficacy of our drug products, product approvals, product sales, revenues, development timelines, product acquisitions, liquidity and capital resources and trends, and other statements containing forward-looking words, such as, “believes,” “may,” “could,” “would,” “will,” “expects,” “intends,” “estimates,” “anticipates,” “plans,” “seeks,” or “continues” or the negative thereof or variation thereon or similar terminology (although not all forward-looking statements contain these words). Such forward-looking statements are based on the beliefs of our management as well as assumptions made by and information currently available to our management. Readers should not put undue reliance on these forward-looking statements because they involve known and unknown risks, uncertainties and other factors, some of which are beyond our control. These risks, uncertainties and other factors may cause our actual results, performance or achievements to be materially different from the anticipated future results, performance or achievements expressed or implied by the forward-looking statements.

Factors that might cause these differences include the following:

• our ability to successfully develop, obtain regulatory approval for, and market our products;

• the approval, or timing of approval, of our products or new indications for our products by the U.S. Food and Drug Administration (the “FDA”) and other international regulatory agencies;

• actions by the FDA and other regulatory agencies, including international agencies;

• the timing and/or results of pending or future clinical trials, and our reliance on contract research organizations;

• our ability to maintain sufficient cash resources to fund our business operations;

• our history of net losses;

• our ability to enter into strategic alliances with partners for manufacturing, development and commercialization;

• our competitors’ progress with their drug development programs, which could adversely impact the perceived or actual value of our in-development drugs;

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• the ability of our manufacturing partners to meet our product demands and timelines;

• our ability to identify and acquire new product candidates and to successfully integrate those product candidates into our operations;

• our ability to protect our intellectual property rights;

• the impact of legislative or regulatory reform on the pricing for pharmaceutical products;

• the impact of any litigation to which we are, or may become a party;

• our ability, and that of our suppliers, development partners, and manufacturing partners, to comply with laws, regulations and standards that govern or affect the pharmaceutical and biotechnology industries; and

• our ability to maintain the services of our key executives and other personnel.

We urge you to consider these factors carefully in evaluating the forward-looking statements contained in this prospectus and any prospectus supplement. All subsequent written or oral forward-looking statements attributable to our company or persons acting on our behalf are expressly qualified in their entirety by these cautionary statements. The forward-looking statements included in this prospectus are made only as of the date of this prospectus. We undertake no obligation to update publicly any forward-looking statements, whether as a result of new information, future events or otherwise, except to the extent that we are required to do so by law.

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USE OF PROCEEDS

Unless we indicate otherwise in the applicable prospectus supplement, we anticipate that the net proceeds from the sale of the securities offered from time to time hereby will be used for general corporate purposes, including, without limitation, research and development and clinical development costs to support the advancement of our in-development drug candidates, activities in connection with the launch of our in-development drug candidates, including hiring and building inventory supply, making acquisitions of assets, businesses, companies or securities, capital expenditures and for working capital. When a particular series of securities is offered, the related prospectus supplement will set forth our intended use of the net proceeds we receive from the sale of the securities. Pending the application of the net proceeds, we may invest the proceeds in short-term, interest-bearing instruments or other investment-grade securities.

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DESCRIPTION OF CAPITAL STOCK WE MAY OFFER

General

Our authorized capital stock consists of 300,000,000 shares of common stock, par value $0.001 per share, and 5,000,000 shares of preferred stock, par value $0.001 per share.

The following description of our common stock and preferred stock, together with the additional information included in any applicable prospectus supplements or related free writing prospectuses, summarizes the material terms and provisions of these types of securities, but it is not complete. For the complete terms of our common stock and preferred stock, please refer to our restated certificate of incorporation and our third amended and restated bylaws that are incorporated by reference into the Registration Statement which includes this prospectus and, with respect to preferred stock, any certificate of designation that we may file with the SEC for a series of preferred stock we may designate, if any.

We will describe in a prospectus supplement or related free writing prospectuses, the specific terms of any common stock or preferred stock we may offer pursuant to this prospectus. If indicated in a prospectus supplement, the terms of such common stock or preferred stock may differ from the terms described below.

Common Stock

As of May 4, 2020, there were 116,468,472 shares of common stock outstanding. The holders of our common stock are entitled to one vote for each share held of record on all matters submitted to a vote of the stockholders. The holders of common stock are not entitled to cumulative voting rights with respect to the election of directors, and as a consequence, minority stockholders will not be able to elect directors on the basis of their votes alone.

Subject to preferences that may be applicable to any then outstanding shares of preferred stock, holders of common stock are entitled to receive ratably such dividends as may be declared by the board of directors out of funds legally available therefor. In the event of a liquidation, dissolution or winding up of us, holders of the common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preferences of any then outstanding shares of preferred stock. Holders of common stock have no preemptive rights and no right to convert their common stock into any other securities. There are no redemption or sinking fund provisions applicable to our common stock. All outstanding shares of common stock are, and all shares of common stock to be issued under this prospectus will be, fully paid and non-assessable. The rights, preferences and privileges of holders of our common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any of our outstanding preferred stock.

Listing

Our common stock is listed under the symbol “SPPI” on the NASDAQ.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A.

Dividends

We have not declared any cash dividends on our common stock since 2012 and we do not anticipate paying any cash dividends on our common stock in the foreseeable future.

Stockholder Rights Agreement

On November 29, 2010, our board of directors approved a stockholder rights agreement, effective December 13, 2010, or the Stockholder Rights Agreement. A stockholder rights agreement is designed to deter

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coercive, unfair, or inadequate takeovers and other abusive tactics that might be used in an attempt to gain control of our company. The Stockholder Rights Agreement will not prevent takeovers at a full and fair price, but rather is designed to deter coercive takeover tactics and to encourage anyone attempting to acquire our company to first negotiate with our board of directors.

On March 27, 2018, we entered into a Second Amendment to the Stockholder Rights Agreement which had the effect of suspending the Stockholders Rights Agreement as of March 30, 2018, though it will expire under its terms on December 13, 2020.

Preferred Stock

We are authorized to issue a total of 5,000,000 shares of preferred stock. As of May 4, 2020, there were no shares of preferred stock issued and outstanding.

Preferred stock may be issued from time to time, in one or more series, as authorized by the board of directors, without stockholder approval. The prospectus supplement relating to the preferred shares offered thereby will include specific terms of any preferred shares offered, including, if applicable:

• the title of the shares of preferred stock;

• the number of shares of preferred stock offered, the liquidation preference per share and the offering price of the shares of preferred stock;

• the dividend rate(s), period(s) and/or payment date(s) or method(s) of calculation thereof applicable to the shares of preferred stock;

• whether the shares of preferred stock are cumulative or not and, if cumulative, the date from which dividends on the shares of preferred stock shall accumulate;

• the procedures for any auction and remarketing, if any, for the shares of preferred stock;

• the provision for a sinking fund, if any, for the shares of preferred stock;

• the provision for redemption or repurchase, if applicable, and any restrictions on our ability to exercise those redemption and repurchase rights of the shares of preferred stock;

• any listing of the shares of preferred stock on any securities exchange;

• the terms and conditions, if applicable, upon which the shares of preferred stock will be convertible into common shares, including the conversion price (or manner of calculation thereof);

• discussion of federal income tax considerations applicable to the shares of preferred stock;

• the relative ranking and preferences of the shares of preferred stock as to dividend rights and rights upon liquidation, dissolution or winding up of our affairs;

• any limitations on issuance of any series or class of shares of preferred stock ranking senior to or on a parity with such series or class of shares of preferred stock as to dividend rights and rights upon liquidation, dissolution or winding up of our affairs;

• any other specific terms, preferences, rights, limitations or restrictions of the shares of preferred stock; and

• any voting rights of such preferred stock.

The transfer agent and registrar for any series or class of preferred stock will be set forth in the applicable prospectus supplement.

Possible Anti-Takeover Effects of Delaware Law and our Charter Documents

Provisions of the Delaware General Corporation Law, or DGCL, our restated certificate of incorporation, and our third amended and restated bylaws, could make it more difficult to acquire us by means of a tender offer,

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a proxy contest or otherwise, or to remove incumbent officers and directors. These provisions, summarized below, are expected to discourage certain types of coercive takeover practices and takeover bids that our board of directors may consider inadequate and to encourage persons seeking to acquire control of us to first negotiate with our board of directors. We believe that the benefits of increased protection of our ability to negotiate with the proponent of an unfriendly or unsolicited proposal to acquire or restructure us outweigh the disadvantages of discouraging takeover or acquisition proposals because, among other things, negotiation of these proposals could result in an improvement of their terms.

Delaware Anti-Takeover Statute

We are subject to Section 203 of the DGCL, an anti-takeover statute. In general, Section 203 of the DGCL prohibits a publicly held Delaware corporation from engaging in a “business combination” with an “interested stockholder” for a period of three years following the time the person became an interested stockholder, unless the business combination or the acquisition of shares that resulted in a stockholder becoming an interested stockholder is approved in a prescribed manner. Generally, a “business combination” includes a merger, asset or stock sale, or other transaction resulting in a financial benefit to the interested stockholder. Generally, an “interested stockholder” is a person who, together with affiliates and associates, owns (or within three years prior to the determination of interested stockholder status did own) 15% or more of a corporation’s voting stock. The existence of this provision would be expected to have an anti-takeover effect with respect to transactions not approved in advance by our board of directors, including discouraging attempts that might result in a premium over the market price for the shares of common stock held by our stockholders.

Election and Removal of Directors

Our board of directors is elected annually by all holders of our capital stock. The stockholders may nominate one or more persons for election as directors at an annual meeting of stockholders, but only if written notice of such stockholder’s intent to make such nomination or nominations has been received by the Secretary of the Company not less than ninety (90) nor more than one hundred twenty (120) days prior to the first anniversary of the preceding year’s annual meeting of stockholders. Any vacancy on the board of directors resulting from death, resignation, removal or otherwise or newly created directorships may be filled by the vote of the majority of directors then in office, although less than a quorum, or by a sole remaining director.

Amendment

The affirmative vote of a majority of the entire board of directors may amend and repeal the bylaws. The bylaws may be altered, amended or repealed, and new bylaws may be adopted, at any annual meeting of the stockholders (or at any special meeting thereof duly called for that purpose) by a majority of the combined voting power of the then outstanding shares of capital stock of all classes and series of the Company entitled to vote generally in the election of directors, voting as a single class, provided that, in the notice of any such special meeting, notice of such purpose shall be given.

Size of Board and Vacancies

Pursuant to our restated certificate of incorporation, and our third amended and restated bylaws, our board of directors has the exclusive right to fix the size of the board and to fill any vacancies resulting from death, resignation, disqualification or removal as well as any newly created directorships arising from an increase in the size of the board.

Special Stockholder Meetings

Our third amended and restated bylaws provide that special meetings of stockholders can be called only by the board of directors, the chairman of the board of directors or the chief executive officer. Stockholders are not permitted to call a special meeting and cannot require the board of directors to call a special meeting. There is no right of stockholders to act by written consent without a meeting, unless the consent is unanimous.

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Stockholder Action by Unanimous Written Consent

Any action which may be taken at any annual or special meeting of stockholders, may be taken without a meeting and without prior notice, if a consent in writing or by electronic communication, setting forth the action so taken, is given by the holders of all of the outstanding shares entitled to vote thereon.

Requirements for Advance Notification of Stockholder Nominations and Proposals

Our third amended and restated bylaws establish advance notice procedures with respect to stockholder proposals and nomination of candidates for election as directors other than nominations made by or at the direction of our board of directors or a committee of our board of directors.

No Cumulative Voting

The DGCL provides that stockholders are denied the right to cumulate votes in the election of directors unless our certificate of incorporation provides otherwise. Our restated certificate of incorporation does not provide for cumulative voting.

Authorized but Unissued Shares

Our authorized but unissued shares of common stock and preferred stock will be available for future issuance without stockholder approval. We may use additional shares for a variety of purposes, including future public offerings to raise additional capital, to fund acquisitions and as employee compensation. The existence of authorized but unissued shares of undesignated preferred stock may enable our board of directors to render more difficult or to discourage an attempt to obtain control of us by means of a merger, tender offer, proxy contest or otherwise. For example, if in the due exercise of its fiduciary obligations, our board of directors were to determine that a takeover proposal is not in the best interests of us or our stockholders, our board of directors could cause shares of preferred stock to be issued without stockholder approval in one or more private offerings or other transactions that might dilute the voting or other rights of the proposed acquirer, stockholder or stockholder group. The rights of holders of our common stock described above will be subject to, and may be adversely affected by, the rights of any preferred stock that we may designate and issue in the future. The issuance of shares of undesignated preferred stock could decrease the amount of earnings and assets available for distribution to holders of shares of common stock. The issuance may also adversely affect the rights and powers, including voting rights, of these holders and may have the effect of delaying, deterring or preventing a change in control of us.

Director Liability

Our third amended and restated bylaws limit the extent to which our directors are personally liable to us and our stockholders, to the fullest extent permitted by the DGCL. The inclusion of this provision in our third amended and restated bylaws may reduce the likelihood of derivative litigation against directors and may discourage or deter stockholders or management from bringing a lawsuit against directors for breach of their duty of care.

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DESCRIPTION OF DEBT SECURITIES WE MAY OFFER

The following description, together with the additional information we include in any applicable prospectus supplements or free writing prospectuses, summarizes the material terms and provisions of the debt securities that we may offer under this prospectus. We may issue debt securities, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. While the terms we have summarized below will apply generally to any future debt securities we may offer under this prospectus, we will describe the particular terms of any debt securities that we may offer in more detail in the applicable prospectus supplement or free writing prospectus. The terms of any debt securities we offer under a prospectus supplement may differ from the terms we describe below. Unless the context requires otherwise, whenever we refer to the “indentures,” we also are referring to any supplemental indentures that specify the terms of a particular series of debt securities.

We will issue any senior debt securities under the senior indenture that we will enter into with the trustee named in the senior indenture. We will issue any subordinated debt securities under the subordinated indenture and any supplemental indentures that we will enter into with the trustee named in the subordinated indenture. We have filed forms of these documents as exhibits to the Registration Statement, of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the Registration Statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

The indentures will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We use the term “trustee” to refer to either the trustee under the senior indenture or the trustee under the subordinated indenture, as applicable.

The following summaries of material provisions of the senior debt securities, the subordinated debt securities and the indentures are subject to, and qualified in their entirety by reference to, all of the provisions of the indenture and any supplemental indentures applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplements and any related free writing prospectuses related to the debt securities that we may offer under this prospectus, as well as the complete indenture that contains the terms of the debt securities. Except as we may otherwise indicate, the terms of the senior indenture and the subordinated indenture are identical.

General

The terms of each series of debt securities will be established by or pursuant to a resolution of our board of directors and set forth or determined in the manner provided in an officers’ certificate or by a supplemental indenture. Debt securities may be issued in separate series without limitation as to aggregate principal amount. We may specify a maximum aggregate principal amount for the debt securities of any series. We will describe in the applicable prospectus supplement the terms of the series of debt securities being offered, including:

• the title;

• the principal amount being offered, and if a series, the total amount authorized and the total amount outstanding;

• any limit on the amount that may be issued;

• whether or not we will issue the series of debt securities in global form, and, if so, the terms and who the depositary will be;

• the maturity date;

• whether and under what circumstances, if any, we will pay additional amounts on any debt securities held by a person who is not a U.S. person for tax purposes, and whether we can redeem the debt securities if we have to pay such additional amounts;

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• the annual interest rate, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;

• whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;

• the terms of the subordination of any series of subordinated debt;

• the place where payments will be payable;

• restrictions on transfer, sale or other assignment, if any;

• our right, if any, to defer payment of interest and the maximum length of any such deferral period;

• the date, if any, after which, and the price at which, we may, at our option, redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemption provisions;

• provisions for a sinking fund purchase or other analogous fund, if any, including the date, if any, on which, and the price at which we are obligated, pursuant thereto or otherwise, to redeem, or at the holder’s option, to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;

• provisions relating to modification of the terms of the security or the rights of the security holder;

• whether the indenture will restrict our ability or the ability of our subsidiaries to:

• incur additional indebtedness;

• issue additional securities;

• create liens;

• pay dividends or make distributions in respect of our capital stock or the capital stock of our subsidiaries;

• redeem capital stock;

• place restrictions on our subsidiaries’ ability to pay dividends, make distributions or transfer assets;

• make investments or other restricted payments;

• sell, transfer or otherwise dispose of assets;

• enter into sale-leaseback transactions;

• engage in transactions with stockholders or affiliates;

• issue or sell stock of our subsidiaries; or

• effect a consolidation or merger;

• whether the indenture will require us to maintain any interest coverage, fixed charge, cash flow-based, asset-based or other financial ratios;

• information describing any book-entry features;

• the applicability of the provisions in the indenture on discharge;

• whether the debt securities are to be offered at a price such that they will be deemed to be offered at an “original issue discount” as defined in paragraph (a) of Section 1273 of the Internal Revenue Code of 1986, as amended;

• the denominations in which we will issue the series of debt securities, if other than denominations of $1,000 and any integral multiple thereof;

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• the currency of payment of debt securities if other than U.S. dollars and the manner of determining the equivalent amount in U.S. dollars; and

• any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, including any additional events of default or covenants provided with respect to the debt securities, and any terms that may be required by us or advisable under applicable laws or regulations.

U.S. federal income tax consequences applicable to debt securities sold at an original issue discount will be described in the applicable prospectus supplement. In addition, U.S. federal income tax or other consequences applicable to any debt securities which are denominated in a currency or currency unit other than U.S. dollars may be described in the applicable prospectus supplement.

Conversion or Exchange Rights

We will set forth in the applicable prospectus supplement the terms under which a series of debt securities may be convertible into or exchangeable for our common stock, our preferred stock or other securities (including securities of a third party). We will include provisions as to whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock, our preferred stock or other securities (including securities of a third party) that the holders of the series of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the indentures will not contain any covenant that restricts our ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of all or substantially all of our assets. However, any successor to or acquiror of such assets must assume all of our obligations under the indentures or the debt securities, as appropriate. If the debt securities are convertible into or exchangeable for our other securities or securities of other entities, the person with whom we consolidate or merge or to whom we sell all of our property must make provisions for the conversion of the debt securities into securities that the holders of the debt securities would have received if they had converted the debt securities before the consolidation, merger or sale.

Events of Default under the Indenture

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the following are events of default under the indentures with respect to any series of debt securities that we may issue:

• if we fail to pay interest when due and payable and our failure continues for 90 days and the time for payment has not been extended;

• if we fail to pay the principal, premium or sinking fund payment, if any, when due and payable and the time for payment has not been extended;

• if we fail to observe or perform any other covenant contained in the debt securities or the indentures, other than a covenant specifically relating to another series of debt securities, and our failure continues for 90 days after we receive notice from the trustee or we and the trustee receive notice from the holders of at least 25% in aggregate principal amount of the outstanding debt securities of the applicable series; and

• if specified events of bankruptcy, insolvency or reorganization occur.

We will describe in each applicable prospectus supplement any additional events of default relating to the relevant series of debt securities. If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the trustee or the holders of at

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least 25% in aggregate principal amount of the outstanding debt securities of that series, by notice to us in writing, and to the trustee if notice is given by such holders, may declare the unpaid principal, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default arises due to the occurrence of certain specified bankruptcy, insolvency or reorganization events, the unpaid principal, premium, if any, and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.

The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any such waiver shall cure the default or event of default.

Subject to the terms of the applicable indenture, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity or security satisfactory to it against any loss, liability or expense. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series, provided that:

• the direction so given by the holders is not in conflict with any law or the applicable indenture; and

• subject to its duties under the Trust Indenture Act, the trustee need not take any action that might involve it in personal liability or might be unduly prejudicial to the holders not involved in the proceeding.

The indentures provide that if an event of default has occurred and is continuing, the trustee will be required in the exercise of its powers to use the degree of care that a prudent person would use in the conduct of its own affairs. The trustee, however, may refuse to follow any direction that conflicts with law or the indenture, or that the trustee determines is unduly prejudicial to the rights of any other holder of the relevant series of debt securities, or that would involve the trustee in personal liability. Prior to taking any action under the indentures, the trustee will be entitled to indemnification against all costs, expenses and liabilities that would be incurred by taking or not taking such action.

A holder of the debt securities of any series will have the right to institute a proceeding under the indentures or to appoint a receiver or trustee, or to seek other remedies only if:

• the holder has given written notice to the trustee of a continuing event of default with respect to that series;

• the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made a written request and such holders have offered reasonable indemnity to the trustee or security satisfactory to it against any loss, liability or expense to be incurred in compliance with instituting the proceeding as trustee; and

• the trustee does not institute the proceeding, and does not receive from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series other conflicting directions within 60 days after the notice, request and offer.

These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities.

We will periodically file statements with the trustee regarding our compliance with specified covenants in the indentures.

The indentures provide that if a default occurs and is continuing and is actually known to a responsible officer of the trustee, the trustee must mail to each holder notice of the default within 45 days after it occurs,

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unless such default has been cured. Except in the case of a default in the payment of principal or premium of, or interest on, any debt security or certain other defaults specified in an indenture, the trustee shall be protected in withholding such notice if and so long as the board of directors, the executive committee or a trust committee of directors, or responsible officers of the trustee, in good faith determine that withholding notice is in the best interests of holders of the relevant series of debt securities.

Modification of Indenture; Waiver

Subject to the terms of the indenture for any series of debt securities that we may issue, we and the trustee may change an indenture without the consent of any holders with respect to the following specific matters:

• to fix any ambiguity, defect or inconsistency in the indenture;

• to comply with the provisions described above under “—Consolidation, Merger or Sale”;

• to comply with any requirements of the SEC in connection with the qualification of any indenture under the Trust Indenture Act;

• to add to, delete from or revise the conditions, limitations and restrictions on the authorized amount, terms or purposes of issue, authentication and delivery of debt securities, as set forth in such indenture;

• to provide for the issuance of, and establish the form and terms and conditions of, the debt securities of any series as provided under “—General,” to establish the form of any certifications required to be furnished pursuant to the terms of the indenture or any series of debt securities, or to add to the rights of the holders of any series of debt securities;

• to evidence and provide for the acceptance of appointment hereunder by a successor trustee;

• to provide for uncertificated debt securities in addition to or in place of certificated debt securities and to make all appropriate changes for such purpose;

• to add such new covenants, restrictions, conditions or provisions for the protection of the holders, and to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default or to surrender any right or power conferred to us in the indenture; or

• to change anything that does not materially adversely affect the interests of any holder of debt securities of any series in any material respect; provided that any amendment made solely to conform the provisions of the indenture to the corresponding description of the debt securities contained in the applicable prospectus or prospectus supplement shall be deemed not to adversely affect the interests of the holders of such debt securities; provided further, that in connection with any such amendment we will provide the trustee with an officers’ certificate certifying that such amendment will not adversely affect the rights or interests of the holders of such debt securities.

In addition, under the indentures, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of at least a majority in aggregate principal amount of the outstanding debt securities of each series that is affected. However, unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, we and the trustee may only make the following changes with the consent of each holder of any outstanding debt securities affected:

• extending the fixed maturity of the series of debt securities;

• reducing the principal amount, reducing the rate of or extending the time of payment of interest, or reducing any premium payable upon the redemption of any debt securities;

• reducing the percentage of debt securities, the holders of which are required to consent to any amendment, supplement, modification or waiver;

• changing any of our obligations to pay additional amounts;

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• reducing the amount of principal of an original issue discount security or any other note payable upon acceleration of the maturity thereof;

• changing the currency in which any note or any premium or interest is payable;

• impairing the right to enforce any payment on or with respect to any note;

• adversely changing the right to convert or exchange, including decreasing the conversion rate or increasing the conversion price of, such note, if applicable;

• in the case of the subordinated indenture, modifying the subordination provisions in a manner adverse to the holders of the subordinated debt securities;

• if the debt securities are secured, changing the terms and conditions pursuant to which the debt securities are secured in a manner adverse to the holders of the secured debt securities;

• reducing the requirements contained in the applicable indenture for quorum or voting;

• changing any of our obligations to maintain an office or agency in the places and for the purposes required by the indentures; or

• modifying any of the above provisions set forth in this paragraph.

Discharge

Each indenture provides that, subject to the terms of the indenture and any limitation otherwise provided in the prospectus supplement applicable to a particular series of debt securities, we may elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

• register the transfer or exchange of debt securities of the series;

• replace stolen, lost or mutilated debt securities of the series;

• maintain paying agencies;

• hold monies for payment in trust;

• recover excess money held by the trustee;

• compensate and indemnify the trustee; and

• appoint any successor trustee.

In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of, and any premium and interest on, the debt securities of the series on the dates payments are due.

Form, Exchange and Transfer

We will issue the debt securities of each series only in fully registered form without coupons and, unless we otherwise specify in the applicable prospectus supplement, in denominations of $1,000 and any integral multiple thereof. The indentures provide that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company or another depositary named by us and identified in a prospectus supplement with respect to that series.

At the option of the holder, subject to the terms of the indentures and the limitations applicable to global securities described in the applicable prospectus supplement, the holder of the debt securities of any series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.

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Subject to the terms of the indentures and the limitations applicable to global securities set forth in the applicable prospectus supplement, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will impose no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

We will name in the applicable prospectus supplement the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

If we elect to redeem the debt securities of any series, we will not be required to:

• issue, register the transfer of, or exchange any debt securities of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption of any debt securities that may be selected for redemption and ending at the close of business on the day of the mailing; or

• register the transfer of or exchange any debt securities so selected for redemption, in whole or in part, except the unredeemed portion of any debt securities we are redeeming in part.

Information Concerning the Trustee

The trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture and is under no obligation to exercise any of the powers given it by the indentures at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur. However, upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs.

Payment and Paying Agents

Unless we otherwise indicate in the applicable prospectus supplement, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest payment.

We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement, we will designate the corporate trust office of the trustee in the City of New York as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

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Governing Law

The indentures and the debt securities will be governed by and construed in accordance with the laws of the State of New York, except to the extent that the Trust Indenture Act is applicable.

Ranking Debt Securities

The subordinated debt securities will be unsecured and will be subordinate and junior in priority of payment to certain of our other indebtedness to the extent described in a prospectus supplement. The subordinated indenture does not limit the amount of subordinated debt securities that we may issue. It also does not limit us from issuing any other secured or unsecured debt.

The senior debt securities will be unsecured and will rank equally in right of payment to all our other senior unsecured debt. The senior indenture does not limit the amount of senior debt securities that we may issue. It also does not limit us from issuing any other secured or unsecured debt.

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DESCRIPTION OF WARRANTS WE MAY OFFER

As of May 4, 2020, we had no warrants to purchase shares of our common stock outstanding. We typically issue warrants to purchase shares of our common stock to investors as part of a financing transaction, or in connection with services rendered by placement agents and outside consultants.

We may issue warrants to purchase debt securities, preferred stock, common stock or any combination of the foregoing. We may issue warrants independently or together with any other securities we offer under a prospectus supplement. The warrants may be attached to or separate from the securities. We will issue each series of warrants under a separate warrant agreement to be entered into between a warrant agent and us. The warrant agent will act solely as our agent in connection with the warrants and will not have any obligations or relationship of agency or trust for or with holders or beneficial owners of warrants. The following outlines some of the general terms and provisions of the warrants that we may issue from time to time. When we issue warrants, we will provide the specific terms of the warrants and the applicable warrant agreement in a prospectus supplement and any related free writing prospectuses and such terms may differ from those described below. To the extent the information contained in the prospectus supplement differs from this summary description, you should rely on the information in the prospectus supplement. The following description, and any description of the warrants included in a prospectus supplement, may not be complete and is subject to and qualified in its entirety by reference to the terms and provisions of the applicable warrant agreement.

Debt Warrants

We will describe in the applicable prospectus supplement and any related free writing prospectuses the terms of the debt warrants being offered, the warrant agreement relating to the debt warrants and the debt warrant certificates representing the debt warrants, including, as applicable:

• the title of the debt warrants;

• the aggregate number of the debt warrants;

• the price or prices at which the debt warrants will be issued;

• the designation, aggregate principal amount and terms of the debt securities purchasable upon exercise of the debt warrants, and the procedures and conditions relating to the exercise of the debt warrants;

• the designation and terms of any related debt securities with which the debt warrants are issued, and the number of the debt warrants issued with each security;

• the date, if any, on and after which the debt warrants and the related debt securities will be separately transferable;

• the principal amount of debt securities purchasable upon exercise of each debt warrant, and the price at which the principal amount of the debt securities may be purchased upon exercise;

• the date on which the right to exercise the debt warrants will commence, and the date on which the right will expire;

• the maximum or minimum number of the debt warrants that may be exercised at any time;

• information with respect to book-entry procedures, if any;

• changes to or adjustments in the exercise price of the debt warrants;

• a discussion of the material U.S. federal income tax considerations applicable to the exercise of the debt warrants; and

• any other terms of the debt warrants and terms, procedures and limitations relating to the exercise of the debt warrants.

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As may be permitted under the warrant agreement, holders may exchange debt warrant certificates for new debt warrant certificates of different denominations, and may exercise debt warrants at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus supplement and any related free writing prospectuses. Prior to the exercise of their debt warrants, holders of debt warrants will not have any of the rights of holders of the securities purchasable upon the exercise and will not be entitled to payments of principal, premium or interest on the securities purchasable upon the exercise of debt warrants.

Equity Warrants

We will describe in the applicable prospectus supplement and any related free writing prospectuses the terms of the preferred stock warrants or common stock warrants being offered, the warrant agreement relating to the preferred stock warrants or common stock warrants and the warrant certificates representing the preferred stock warrants or common stock warrants, including, as applicable:

• the title of the warrants;

• the securities for which the warrants are exercisable;

• the price or prices at which the warrants will be issued;

• if applicable, the number of warrants issued with each share of preferred stock or share of common stock;

• if applicable, the date on and after which the warrants and the related preferred stock or common stock will be separately transferable;

• the date on which the right to exercise the warrants will commence, and the date on which the right will expire;

• the maximum or minimum number of warrants which may be exercised at any time;

• information with respect to book-entry procedures, if any;

• a discussion of the material U.S. federal income tax considerations applicable to exercise of the warrants; and

• any other terms of the warrants, including terms, procedures and limitations relating to the exchange and exercise of the warrants.

Unless otherwise provided in the applicable warrant agreement and corresponding prospectus supplement or any related free writing prospectuses, holders of equity warrants will not be entitled, by virtue of being such holders, to vote, consent, receive dividends, receive notice as stockholders with respect to any meeting of stockholders for the election of our directors or any other matter, or to exercise any rights whatsoever as stockholders.

Except as provided in the applicable warrant agreement and corresponding prospectus supplement or any related free writing prospectuses, the exercise price payable and the number of shares of common stock or preferred stock purchasable upon the exercise of each warrant will be subject to adjustment in certain events, including the issuance of a stock dividend to holders of common stock or preferred stock or a stock split, reverse stock split, combination, subdivision or reclassification of common stock or preferred stock. In lieu of adjusting the number of shares of common stock or preferred stock purchasable upon exercise of each warrant, we may elect to adjust the number of warrants. Unless otherwise provided in the applicable warrant agreement and corresponding prospectus supplement or any related free writing prospectuses, no adjustments in the number of shares purchasable upon exercise of the warrants will be required until all cumulative adjustments require an adjustment of at least 1% thereof. No fractional shares will be issued upon exercise of warrants, but we will pay the cash value of any fractional shares otherwise issuable. Notwithstanding the foregoing, except as otherwise provided in the applicable warrant agreement and corresponding prospectus supplement or any related free writing prospectuses, in case of any consolidation, merger, or sale or conveyance of our property as an entirety or

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substantially as an entirety, the holder of each outstanding warrant will have the right to the kind and amount of shares of stock and other securities and property, including cash, receivable by a holder of the number of shares of common stock or preferred stock into which each warrant was exercisable immediately prior to the particular triggering event.

Exercise of Warrants

Each warrant will entitle the holder of the warrant to purchase for cash at the exercise price provided in the applicable warrant agreement and corresponding prospectus supplement or any related free writing prospectuses the principal amount of debt securities or shares of preferred stock or shares of common stock being offered. Holders may exercise warrants at any time up to the close of business on the expiration date provided in the applicable warrant agreement and corresponding prospectus supplement or any related free writing prospectuses. After the close of business on the expiration date, unexercised warrants are void.

Holders may exercise warrants as described in the applicable warrant agreement and corresponding prospectus supplement or any free writing prospectuses relating to the warrants being offered. Upon receipt of payment and the warrant certificate properly completed and duly executed at the corporate trust office of the warrant agent or any other office indicated in the applicable warrant agreement and corresponding prospectus supplement or any related free writing prospectuses, we will, as soon as practicable, forward the debt securities, shares of preferred stock or shares of common stock purchasable upon the exercise of the warrant. If less than all of the warrants represented by the warrant certificate are exercised, we will issue a new warrant certificate for the remaining warrants.

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DESCRIPTION OF UNITS WE MAY OFFER

The following description, together with the additional information we may include in any applicable prospectus supplements and free writing prospectuses, summarizes the material terms and provisions of the units that we may offer under this prospectus. While the terms we have summarized below will apply generally to any units that we may offer under this prospectus, we will describe the particular terms of any series of units in more detail in the applicable prospectus supplement. The terms of any units offered under a prospectus supplement may differ from the terms described below. However, no prospectus supplement will fundamentally change the terms that are set forth in this prospectus or offer a security that is not registered and described in this prospectus at the time of its effectiveness.

We will file as exhibits to the Registration Statement of which this prospectus is a part, or will incorporate by reference from a current report on Form 8-K that we file with the SEC, the form of unit agreement that describes the terms of the series of units we are offering, and any supplemental agreements, before the issuance of the related series of units. The following summaries of material terms and provisions of the units are subject to, and qualified in their entirety by reference to, all the provisions of the unit agreement and any supplemental agreements applicable to a particular series of units. We urge you to read the applicable prospectus supplements related to the particular series of units that we sell under this prospectus, as well as the complete unit agreement and any supplemental agreements that contain the terms of the units.

General

We may issue units comprised of one or more shares of common stock, shares of preferred stock, debt securities and warrants in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately, at any time or at any time before a specified date.

We will describe in the applicable prospectus supplement the terms of the series of units, including:

• the designation and terms of the units and of the securities comprising the units, including whether and under what circumstances those securities may be held or transferred separately;

• any provisions of the governing unit agreement that differ from those described below; and

• any provisions for the issuance, payment, settlement, transfer or exchange of the units or of the securities comprising the units.

The provisions described in this section, as well as those described under “Description of Capital Stock We May Offer,” “Description of Debt Securities We May Offer” and “Description of Warrants We May Offer” will apply to each unit and to any common stock, preferred stock, debt security or warrant included in each unit, respectively.

Issuance in Series

We may issue units in such amounts and in numerous distinct series as we determine.

Enforceability of Rights by Holders of Units

Each unit agent will act solely as our agent under the applicable unit agreement and will not assume any obligation or relationship of agency or trust with any holder of any unit. A single bank or trust company may act as unit agent for more than one series of units. A unit agent will have no duty or responsibility in case of any default by us under the applicable unit agreement or unit, including any duty or responsibility to initiate any

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proceedings at law or otherwise, or to make any demand upon us. Any holder of a unit may, without the consent of the related unit agent or the holder of any other unit, enforce by appropriate legal action its rights as holder under any security included in the unit.

We, the unit agents and any of their agents may treat the registered holder of any unit certificate as an absolute owner of the units evidenced by that certificate for any purpose and as the person entitled to exercise the rights attaching to the units so registered, despite any notice to the contrary.

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PLAN OF DISTRIBUTION

We may sell the offered securities from time to time.

• through agents;

• to or through underwriters;

• to or through broker-dealers (acting as agent or principal);

• in “at the market offerings” within the meaning of Rule 415(a)(4) of the Securities Act;

• directly to purchasers, through a specific bidding or auction process or otherwise; or

• through a combination of these methods of sale.

The applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) will describe the terms of the offering of the securities, including:

• the name or names of any underwriters, if any, and if required, any dealers or agents and the amount of shares underwritten or purchased by each of them;

• the purchase price or other consideration to be paid in connection with the sale of the securities being offered and the proceeds we will receive from the sale;

• any underwriting discounts or agency fees and other items constituting underwriters’ or agents’ compensation;

• any over-allotment options under which underwriters may purchase additional securities from us;

• any discounts or concessions allowed or reallowed or paid to dealers; and

• any securities exchange or market on which the securities may be listed.

We may distribute the securities from time to time in one or more transactions at:

• fixed price or prices, which may be changed from time to time;

• market prices prevailing at the time of sale;

• prices related to such prevailing market prices; or

• negotiated prices.

Only underwriters named in the prospectus supplement are underwriters of the securities offered by the prospectus supplement.

If we utilize an underwriter in the sale of the securities being offered, we will execute an underwriting agreement with the underwriter at the time of sale. Any underwriters used in the sale will acquire the securities for their own account and may resell the securities from time to time in one or more transactions at a fixed public offering price or at varying prices determined at the time of sale. The obligations of the underwriters to purchase the securities will be subject to the conditions set forth in the applicable underwriting agreement. We may offer the securities to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate.

In connection with the sale of the securities, we, or the purchasers of the securities for whom the underwriter may act as agent, may compensate the underwriter in the form of underwriting discounts or commissions. The underwriter may sell the securities to or through dealers, and the underwriter may compensate those dealers in the form of discounts, concessions or commissions. Subject to certain conditions, the underwriters will be obligated to purchase all of the securities offered by the prospectus supplement. We may change from time to time the public offering price and any discounts or concessions allowed or reallowed or paid to dealers.

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We may directly solicit offers to purchase the securities. We may also designate agents to solicit offers to purchase the securities from time to time. We will name in a prospectus supplement any agent involved in the offer or sale of our securities. Unless the prospectus supplement states otherwise, our agent will act on a best-efforts basis for the period of its appointment.

If we utilize a dealer in the sale of the securities being offered by this prospectus, we will sell the securities to the dealer, as principal. The dealer may then resell the securities to the public at varying prices to be determined by the dealer at the time of resale.

We may authorize agents or underwriters to solicit offers by institutional investors to purchase securities from us at the public offering price set forth in the prospectus supplement pursuant to delayed delivery contracts providing for payment and delivery on a specified date in the future. We will describe the conditions to these contracts and the commissions we must pay for solicitation of these contracts in the prospectus supplement.

Underwriters, dealers and agents participating in the distribution of the securities may be deemed to be underwriters within the meaning of the Securities Act, and any discounts and commissions received by them and any profit realized by them on resale of the securities may be deemed to be underwriting discounts and commissions. We may enter into agreements to indemnify underwriters, dealers and agents against civil liabilities, including liabilities under the Securities Act, or to contribute to payments they may be required to make in respect thereof.

In addition, we may enter into derivative transactions with third parties (including the writing of options), or sell securities not covered by this prospectus to third parties in privately negotiated transactions. If the applicable prospectus supplement indicates, in connection with such a transaction, the third parties may, pursuant to this prospectus and the applicable prospectus supplement, sell securities covered by this prospectus and the applicable prospectus supplement. If so, the third party may use securities borrowed from us or others to settle such sales and may use securities received from us to close out any related short positions. We may also loan or pledge securities covered by this prospectus and the applicable prospectus supplement to third parties, who may sell the loaned securities or, in an event of default in the case of a pledge, sell the pledged securities pursuant to this prospectus and the applicable prospectus supplement. The third party in such sale transactions will be an underwriter and will be identified in the applicable prospectus supplement or in a post-effective amendment.

All securities we offer, other than common stock, will be new issues of securities with no established trading market. Any underwriters may make a market in these securities, but will not be obligated to do so and may discontinue any market making at any time without notice. We cannot guarantee the liquidity of the trading markets for any securities. Shares of our common stock sold pursuant to the Registration Statement of which this prospectus is a part will be authorized for listing and trading on the NASDAQ. The applicable prospectus supplement will contain information, where applicable, as to any other listing, if any, on the NASDAQ or any securities market or other securities exchange of the securities covered by the prospectus supplement.

Underwriters may engage in stabilizing and syndicate covering transactions in accordance with Rule 104 under the Exchange Act. Rule 104 permits stabilizing bids to purchase the securities being offered as long as the stabilizing bids do not exceed a specified maximum. Underwriters may over-allot the offered securities in connection with the offering, thus creating a short position in their account. Syndicate covering transactions involve purchases of the offered securities by underwriters in the open market after the distribution has been completed in order to cover syndicate short positions. Underwriters may also cover an over-allotment or short position by exercising their over-allotment option, if any. Stabilizing and syndicate covering transactions may cause the price of the offered securities to be higher than it would otherwise be in the absence of these transactions. These transactions, if commenced, may be discontinued at any time.

Any underwriters who are qualified market makers on the NASDAQ may engage in passive market making transactions in the securities on the NASDAQ in accordance with Rule 103 of Regulation M, during the business

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day prior to the pricing of the offering, before the commencement of offers or sales of the common stock. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded.

The underwriters, dealers and agents may engage in other transactions with us, or perform other services for us, in the ordinary course of their business. We will describe such relationships in the prospectus supplement naming the underwriter and the nature of any such relationship.

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LEGAL MATTERS

The validity of the securities being offered hereby will be passed on by Paul Hastings, LLP, San Diego, California. Any underwriters, dealers or agents will also be advised about the validity of the securities and other legal matters by their own counsel, which will be named in the prospectus supplement.

EXPERTS

The financial statements, and the related financial statement schedule, incorporated in this prospectus by reference from the Company’s Annual Report on Form 10-K, and the effectiveness of Spectrum Pharmaceuticals, Inc.’s internal control over financial reporting have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their reports, which are incorporated herein by reference. Such financial statements and financial statement schedule have been so incorporated in reliance upon the reports of such firm given upon their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We are a reporting company and file annual, quarterly and current reports, proxy and information statements and other information with the SEC. This prospectus is part of a Registration Statement that we have filed with the SEC relating to the securities to be offered under this prospectus. This prospectus does not contain all of the information set forth in the Registration Statement and the exhibits to the Registration Statement. For further information with respect to us and the securities to be offered under this prospectus, we refer you to the Registration Statement and the exhibits and schedules filed as a part of the Registration Statement. The SEC maintains an internet site that contains reports, proxy and information statements, and other information regarding issuers that file electronically with the SEC, where you may read and copy the Registration Statement, as well as our reports, proxy and information statements and other information. The address of the SEC’s web site is www.sec.gov. We maintain a website at www.spprix.com. Information contained in or accessible through our website does not constitute a part of this prospectus.

In addition, our common stock is listed on the NASDAQ and similar information concerning us can be inspected and copied at the offices of The Nasdaq Stock Market, One Liberty Plaza, 165 Broadway, New York, NY 10006.

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INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The SEC allows us to “incorporate by reference” information into this prospectus. This means that we can disclose important information about us and our financial condition to you by referring you to another document filed separately with the SEC. The information incorporated by reference is considered to be part of this prospectus. This prospectus incorporates by reference the documents listed below that we have previously filed with the SEC:

• Our Annual Report on Form 10-K for the fiscal year ended December 31, 2019, as filed with the SEC on March 2, 2020;

• Our Definitive Proxy Statement on Schedule 14A, as filed with the SEC on April  22, 2020 (to the extent incorporated by reference into Part III of our Annual Report on Form 10-K for the fiscal year ended December 31, 2019);

• Our Current Reports on Form 8-K, as filed with the SEC on March  13, 2020 and April 23, 2020; and

• The description of our common stock contained in the Registration of Securities of Certain Successor Issuers filed pursuant to Section 12(g) of the Exchange Act on Form 8-B on June 27, 1997, including any amendment or reports filed for the purpose of updating such description.

We also incorporate by reference into this prospectus all documents filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, including any such documents filed after the date of the initial registration statement and prior to the effectiveness date of the registration statement, until we file a post-effective amendment which indicates that all securities offered hereby have been sold or which deregisters all securities then remaining unsold. Nothing in this prospectus shall be deemed to incorporate information furnished but not filed with the SEC (including without limitation, information furnished under Item 2.02 or Item 7.01 of Form 8-K, and any exhibits relating to such information).

Any statement contained in this prospectus or in a document incorporated or deemed to be incorporated by reference in this prospectus shall be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained herein or in the applicable prospectus supplement or in any other subsequently filed document which also is or is deemed to be incorporated by reference modifies or supersedes the statement. Any statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

We will provide to each person, including any beneficial owner, to whom a prospectus is delivered, upon written or oral request, at no cost to the requestor, a copy of any or all of the information that is incorporated by reference in this prospectus. Requests for such documents should be directed to:

Spectrum Pharmaceuticals, Inc.

11500 South Eastern Avenue, Suite 240

Henderson, Nevada 89052

Telephone: (702) 835-6300

Attention: Investor Relations

Statements contained in this prospectus as to the contents of any contract or other documents are not necessarily complete, and in each instance investors are referred to the copy of the contract or other document filed as an exhibit to the Registration Statement, each such statement being qualified in all respects by such reference and the exhibits and schedules thereto.

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Up to $60,000,000

Common Stock

PROSPECTUS

Cantor H.C. Wainwright & Co. B. Riley Securities

November 6, 2020