Five Prime Therapeutics Announces Option Exercise by GlaxoSmithKline for a Commercial License to a Novel Muscle Disease Target

Five Prime Therapeutics, Inc. FPRX, +1.82% (Five Prime), a clinical-stage biotechnology company focused on discovering and developing novel protein therapeutics for cancer and inflammatory diseases, announced today that GlaxoSmithKline (GSK) has exercised its option to obtain an exclusive, worldwide license to products containing or directed to an undisclosed muscle disease target that Five Prime discovered using its proprietary library of human extracellular proteins and target screening and discovery capabilities.

Five Prime and GSK established the collaboration in 2010 to enable the potential discovery, development and commercialization of drug targets for skeletal muscle diseases using Five Prime's protein target discovery platform. By exercising its option, GSK will receive exclusive rights to develop and commercialize products globally, at its own cost and expense, that incorporate or are directed to the selected target. Five Prime will receive a payment of $1.5 million in connection with the option exercise and is entitled to receive up to $122.5 million in preclinical, development and commercial-related milestone payments and royalties in the low- to mid-single-digit range on net sales of products related to the target.

"GSK has thoroughly evaluated this muscle disease target and their decision to obtain an exclusive license further validates the strength of our protein discovery platform to identify novel targets in conditions beyond our internal focal areas of cancer and inflammatory diseases," said Lewis T. "Rusty" Williams, M.D., Ph.D., president and chief executive officer of Five Prime. "This novel target has the potential to result in new treatments for patients suffering from skeletal muscle disorders, many of which are not adequately treated by current therapies."

About Five Prime

Five Prime Therapeutics, Inc. discovers and develops innovative therapeutics to improve the lives of patients with serious diseases. Five Prime's comprehensive discovery platform, which encompasses virtually every medically relevant extracellular protein, positions it to explore pathways in cancer, inflammation and their intersection in cancer immunotherapy, an area of oncology with significant therapeutic potential and a growing focus of the company's R&D activities. Five Prime has entered into strategic collaborations with leading global pharmaceutical companies and has promising product candidates in clinical and late preclinical development. For more information, please visit www.fiveprime.com.

Cautionary Note on Forward-looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "may," "will," "expect," "plan," "anticipate," "estimate," "intend" and similar expressions (as well as other words or expressions referencing future events, conditions or circumstances) are intended to identify forward-looking statements. These forward-looking statements are based on Five Prime's expectations and assumptions as of the date of this press release. Each of these forward-looking statements involves risks and uncertainties. Actual results may differ materially from these forward-looking statements. Forward-looking statements contained in this press release include statements regarding Five Prime's potential receipt of milestone payments and royalties. Factors that may cause actual results to differ from those expressed or implied in the forward-looking statements in this press release are discussed in Five Prime's filings with the U.S. Securities and Exchange Commission, including the "Risk Factors" contained therein. Except as required by law, Five Prime assumes no obligation to update any forward-looking statements contained herein to reflect any change in expectations, even as new information becomes available.