Five Prime Announces Abstract with Updated Data in Mesothelioma Patients from Ongoing Phase 1b Trial of FP-1039 at ESMO 2017 Congress

• Objective response rate of 48% and disease control rate of 100% in patients at or below the maximum tolerated dose level
  
• Median progression free survival of 7.4 months

SOUTH SAN FRANCISCO, Calif., Sept. 01, 2017 -- Five Prime Therapeutics, Inc. (Nasdaq:FPRX), a clinical-stage biotechnology company focused on discovering and developing innovative immuno-oncology protein therapeutics, announced that updated data from the ongoing Phase 1b trial of FP-1039/GSK3052230 (hereafter FP-1039) in mesothelioma patients were reported today in an abstract submitted to the European Society for Medical Oncology (ESMO) 2017 Congress to be held Sept. 8 – 12, 2017, in Madrid, Spain. The abstract titled “Multicenter, Nonrandomized, Open-Label Phase 1b Study of FP-1039/GSK3052230 with Chemotherapy: Results in Malignant Pleural Mesothelioma (MPM)” by Dr. Jose Trigo et al. is available at http://www.fiveprime.com/news-media/publications-presentations.

The MPM arm of the study evaluated the safety and efficacy of FP-1039 (IV weekly) in combination with standard pemetrexed + cisplatin. The study design involved dose escalation until maximum tolerated dose (MTD) followed by a cohort expansion phase. Endpoints included safety, overall response rate by modified RECIST 1.1, disease control rate (DCR), progression free survival (PFS) and exploratory translational objectives.

As of the cutoff date of March 17, 2017, 36 patients were dosed at 10, 15 and 20 mg/kg doses of FP-1039. Three DLTs were observed at 20 mg/kg but none occurred at 15 mg/kg; therefore, MTD was declared at this dose.

Safety Data

• The most common adverse events (AEs; all grades) observed were: nausea (56%) decreased appetite (36%), fatigue (33%) and infusion reaction (33%).

Efficacy Data

• The confirmed objective response rate (ORR) of all evaluable patients at or below the MTD was 48%, with 13 partial responses in 27 patients.
  
  
• The disease control rate (DCR) was 100%.
  
  
• The median PFS was 7.4 months.

As of May 8, 2017, six patients stayed on the study for over 1 year, of which three were still ongoing.

About FP-1039

FP-1039 is a protein drug designed to intervene in FGF signaling. As a ligand trap, FP-1039 binds to FGF ligands circulating in the extracellular space (such as FGF2), preventing these signaling proteins from reaching FGFR1 on the surface of tumor cells. Treatment with FP-1039 has not been shown to cause hyperphosphatemia, a side effect seen with small molecule inhibitors of FGF receptors, which block the activity of both cancer-associated FGFs and FGF-23. GlaxoSmithKline (GSK) was the sponsor of the trial.

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 immuno-oncology, an area 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.

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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. 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.

CONTACTS:
Heather Rowe
Investor Relations
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