EXHIBIT A

Joint Filing Statement

We, the undersigned, hereby express our agreement that the attached Schedule 13D/A is filed on behalf of each of us.

Dated as September 22, 2016
THE COLUMN GROUP, LP		THE COLUMN GROUP GP, LP
By:	The Column Group GP, LP
By:	/s/ Peter Svennilson	By:	/s/ Peter Svennilson
Name:	Peter Svennilson	Name:	Peter Svennilson
Title:	Managing Partner	Title:	Managing Partner
THE COLUMN GROUP II, LP		THE COLUMN GROUP II GP, LP
By:	The Column Group II GP, LP
By:	/s/ Peter Svennilson	By:	/s/ Peter Svennilson
Name:	Peter Svennilson	Name:	Peter Svennilson
Title:	Managing Partner	Title:	Managing Partner
By:	/s/ Peter Svennilson
	Peter Svennilson
By:	/s/ David V. Goeddel
	David V. Goeddel