Five Prime Begins Dose Expansion In Gastric Cancer Patients With FGFR2b Over-Expression In Phase I Trial Of FPA144

SOUTH SAN FRANCISCO, Calif., Nov. 19, 2015 (GLOBE NEWSWIRE) -- Five Prime Therapeutics, Inc. (Nasdaq:FPRX), a clinical-stage biotechnology company focused on discovering and developing novel protein therapeutics for cancer and inflammatory diseases, announced that the dose escalation part of the ongoing Phase 1 trial of FPA144 has been completed and that dose expansion at has begun at a selected dose in new cohorts of gastric cancer patients whose tumors overexpress FGFR2b. FPA144 is an isoform-selective antibody in development as a targeted therapy for tumors that over-express FGFR2b, and has been engineered for enhanced ADCC, increasing direct tumor cell killing by recruiting natural killer (NK) cells. FGFR2 gene amplification is found in a number of tumors, including approximately 5% of gastric cancers, and is associated with poor prognosis.

Part 1 of the Phase 1 study evaluated the safety and pharmacokinetics (PK) of escalating doses of FPA144 in 27 patients with solid tumors, including unselected gastric cancer patients. Data from Part 1 will be presented at the American Society of Clinical Oncology's (ASCO) 2016 Gastrointestinal Cancers Symposium in San Francisco. The poster entitled, "FPA144-001: A first in human study of FPA 144, an ADCC-enhanced, FGFR2b isoform-selective monoclonal antibody in patients with advanced solid tumors," is scheduled during the session entitled, "Cancers of the Esophagus and Stomach," on Thursday, January 21, 2016 from 12:30-2:00 and 5:30-7:00 Pacific Time. Abstracts are expected to be posted on the meeting website on Tuesday, January 19, 2016.

Enrollment has begun in Part 2 of the trial, evaluating the efficacy of biweekly infusions of FPA144 in approximately 70 metastatic gastric cancer patients, with the aim of exploring the correlation between efficacy and FGFR2b overexpression. Tumor testing for FGFR2b overexpression is being conducted centrally, using a proprietary immunohistochemistry assay. Tumors are also being assessed for FGFR2 gene amplification by FISH analysis. Trial endpoints include safety, pharmacokinetics, response rate and duration of response.

"We are really pleased with the progress we are making in this study and to now be moving into our target population of gastric cancer patients," said Julie Hambleton, M.D., Executive Vice President and Chief Medical Officer of Five Prime. "This is an orphan indication in the U.S. and given the unmet need in this disease and the potential for patients to benefit greatly from new treatment options, we aspire to develop the program expeditiously. In the Phase 1 study, we are already enrolling at global sites, including in Asia where gastric cancer is most prevalent. We are also running preclinical studies to evaluate therapeutic combinations with FPA144 for future testing in gastric cancer patients and to identify other indications that may be suitable for FPA144 therapy."

About FPA144

FPA144 is an anti-FGF receptor 2b (FGFR2b) humanized monoclonal antibody in clinical development as a targeted therapy for tumors that over-express FGFR2b, as determined by a proprietary immunohistochemistry (IHC) diagnostic assay. FPA144 binds specifically to FGFR2b and prevents the binding of certain fibroblast growth factors that promote tumor growth. Additionally, FPA144 has been engineered for enhanced antibody-dependent cell-mediated cytotoxicity (ADCC), increasing direct tumor cell killing by recruiting natural killer (NK) cells. FGFR2 gene amplification (as identified by FISH) is found in a number of tumors, including in approximately 5% of gastric cancer patients, and is associated with poor prognosis.

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 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 about the potential (i) for accelerated development of FPA144 as a monotherapy; (ii) development of FPA144 in combination with other therapeutic agents; and (iii) percent of gastric cancer patients whose tumors are FGFR2 amplified. Many factors may cause differences between current expectations and actual results including unexpected safety or efficacy data observed during preclinical or clinical studies, clinical trial site activation or enrollment rates that are lower than expected, changes in expected or existing competition and changes in the regulatory environment. Other 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.

CONTACT: Amy Kendall, Corporate Communications 415-365-5776 amy.kendall@fiveprime.com