EXHIBIT 99.1

                                                              NEWS RELEASE


Contact: OSI Pharmaceuticals, Inc.          Burns McClellan (representing OSI)
         Kathy Galante                      Kathy Nugent, Ph.D. (media)
         Director                           John Nugent (investors)
         Investor & Public Relations        (212) 213-0006
         (631) 962-2000


               OSI PHARMACEUTICALS ANNOUNCES LAUNCH OF TARCEVA(TM)


MELVILLE, NEW YORK - NOVEMBER 22, 2004- OSI Pharmaceuticals, Inc. (Nasdaq: OSIP)
announced today the initiation of the launch of Tarceva(TM) less than two
business days after last Thursday's approval of the drug for the treatment of
patients with advanced non-small cell lung cancer (NSCLC) after failure of at
least one prior chemotherapy. Tarceva(TM) is priced to wholesalers at $2,026 per
30-day supply of the 150mg tablets, and is also available at 100mg and 25mg
tablet strengths. Tarceva(TM) is approved for use as a monotherapy in second-
and third-line settings and is both the first EGFR inhibitor and the first
non-cytotoxic agent to improve survival in advanced NSCLC patients and to be
approved in the second-line setting.

"We are pleased to be able to make Tarceva available to lung cancer patients so
soon after approval," stated Colin Goddard, Ph.D., Chief Executive Officer of
OSI Pharmaceuticals. "We believe that the broad-based nature of the survival
benefit demonstrated by Tarceva coupled with its side effect profile will make
this a valuable and viable treatment option for lung cancer patients and their
doctors. We also have a strong post-approval development plan seeking to expand
the label and use of Tarceva to earlier stages of lung cancer patients; to other
forms of cancer where EGFR is implicated and where we have seen indications of
activity; and to combinations of all targeted therapies which we believe
represents a true paradigm shift in the treatment of human cancer. With this
plan we are confident that Tarceva can be grown into a major product in the
treatment of a variety of cancers."

The Tarceva(TM) approval was based on the pivotal BR.21 study in 731 patients
with advanced NSCLC. The Tarceva package insert includes a summary of the
Tarceva(TM) data as previously presented at the American Society of Clinical
Oncology 40th annual meeting in New Orleans, La. in May 2004. Tarceva(TM)
demonstrated a survival benefit in essentially all subsets of patients examined
including males and females, patients with adenocarcinoma and squamous cell
histology, patients with good as well as impaired performance status and both
smokers and non-smokers. Median and one-year survival of the overall population
in the BR.21 study was improved by 42.5 (6.7 versus 4.7 months) and 45 percent
(31.2 versus 21.5 percent), respectively, and patients were treated with
Tarceva(TM) for an average of just over four months in the study (23% of
patients were on therapy for more than 6 months). Certain subsets of patients,

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including never smokers and patients who had tumors determined to be EGFR
positive, were seen to have a large survival benefit in response to treatment
with Tarceva(TM). The sub-group of patients who never smoked had a substantial
survival benefit with a hazard ratio of 0.42 (hazard ratio is a measure of the
risk of death and a hazard ratio of <1 indicates a survival benefit). The
sub-group of smokers also had a survival benefit (hazard ratio = 0.87) despite
the fact that this group was also seen to have a 24 percent higher rate of
Tarceva(TM) clearance (higher clearance rates lead to lower levels of exposure
to drug).

The analysis of tumor samples of EGFR expression was conducted on approximately
one-third of the patients in the study for whom tumor samples were available.
Patients whose tumors were EGFR positive exhibited a relatively large survival
benefit (hazard ratio = 0.65). Although patients whose tumors were EGFR negative
did not appear to derive a survival benefit, this group was small and the
statistical confidence levels were wide. In this group 3.2 percent of the
patients did exhibit a tumor response, one measure of anti-tumor activity. In
common with treatment practice the majority of the patients entering the study
did not have tumor samples available to determine EGFR status and the survival
benefit in this group of patients with unknown EGFR status was robust (a hazard
ratio of 0.76). There is no validated test for EGFR in NSCLC and tumor testing
is not required prior to the initiation of therapy with Tarceva(TM).

In the pivotal study, the principal side effects associated with Tarceva(TM) use
are a rash (in 75 percent of patients, with approximately 9 percent of patients
exhibiting grade 3/4 rash) and a generally mild-moderate diarrhea (in 54 percent
of patients, with approximately 6 percent of patients exhibiting grade 3/4
diarrhea). Infrequent reports of serious interstitial lung disease (ILD) have
been observed for patients receiving Tarceva(TM) and other EGFR inhibitors.
However, for Tarceva(TM), there was no difference in the incidence of ILD in the
Tarceva(TM) and placebo arms in the BR.21 study (0.8 percent incidence rate in
both the Tarceva(TM) and placebo arms). Results from two earlier large,
randomized, placebo-controlled clinical trials in first-line advanced NSCLC
patients showed no clinical benefit with concurrent administration of
Tarceva(TM) with doublet platinum-based chemotherapy (carboplatin and paclitaxel
or gemcitabine and cisplatin) and its use is not recommended in that setting.

ABOUT TARCEVA(TM)
Tarceva(TM) is a small molecule designed to target the human epidermal growth
factor receptor 1 (HER1) pathway, which is one of the factors critical to cell
growth in NSCLC. HER1, also known as EGFR, is a component of the HER signaling
pathway, which plays a role in the formation and growth of numerous cancers.
Tarceva(TM) is designed to inhibit the tyrosine kinase activity of the HER1
signaling pathway inside the cell, which may block tumor cell growth. A Phase
III clinical trial of Tarceva(TM) has been completed in pancreatic cancer, and
additional early-stage trials of Tarceva(TM) are being conducted in other solid
tumors.

ABOUT OSI PHARMACEUTICALS
OSI Pharmaceuticals is a leading biotechnology company primarily focused on the
discovery, development, and commercialization of high-quality, next-generation
oncology products that both extend life and improve the quality of life for
cancer patients worldwide. OSI has a balanced pipeline of oncology drug
candidates that includes both novel mechanism-based, gene-targeted therapies
focused in the areas of signal transduction, apoptosis, and a next-generation

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cytotoxic chemotherapy agent. Tarceva(TM), OSI's flagship product, is the first
OSI drug discovered and developed by OSI to obtain FDA approval. OSI exclusively
markets Novantrone(R) (mitoxantrone concentrate for injection) for the approved
oncology indications and Gelclair(R) for the relief of pain associated with oral
mucositis. OSI also established Prosidion Limited, an independently operated
diabetes and obesity subsidiary based in the United Kingdom.


This news release contains forward-looking statements. These statements are
subject to known and unknown risks and uncertainties that may cause actual
future experience and results to differ materially from the statements made.
Factors that might cause such a difference include, among others, the completion
of clinical trials, the FDA review process and other governmental regulation,
OSI's and its collaborators' abilities to successfully develop and commercialize
drug candidates, competition from other pharmaceutical companies, the ability to
effectively market products, and other factors described in OSI Pharmaceuticals'
filings with the Securities and Exchange Commission.


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