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Five Prime Therapeutics Initiates Patient Dosing in The Dose Exploration Cohort of Its Phase 1 Trial of Novel First-in-Class B7-H4 Antibody FPA150

Five Prime Therapeutics, Inc. (Nasdaq: FPRX), a biotechnology company discovering and developing innovative immuno-oncology protein therapeutics, today announced that it initiated patient dosing in the dose exploration cohort of its ongoing Phase 1 clinical trial of FPA150 (FPA150-001; NCT03514121), a targeted, first-in-class immuno-oncology antibody that targets B7-H4.

“We’re excited to be ahead of schedule in opening up our dose exploration basket cohort for FPA150, our first-in-class B7-H4 antibody, in patients whose tumors overexpress B7-H4,” said Helen Collins, M.D., Senior Vice President and Chief Medical Officer of Five Prime. “B7-H4 is generating excitement in investigators because it's expressed in tumor types that are currently not well served by immunotherapy, including breast and gynecologic cancers. We’re hopeful that a targeted therapy like FPA150 will provide clinical benefit in these patients who have limited treatment options.”

B7-H4 is in the same family of checkpoint molecules as PD-L1 and, like PD-L1, appears to inhibit T-cells in preclinical models. FPA150 has a dual mechanism of action: it blocks a T cell checkpoint pathway and delivers antibody-dependent cell-mediated cytotoxicity (ADCC) against B7-H4-expressing tumor cells.

FPA150-001 is an ongoing Phase 1a/1b dose escalation and expansion clinical trial of FPA150 monotherapy in patients with advanced solid tumors. The exploratory basket cohort is a part of that trial and will include up to 10 patients whose tumors overexpress B7-H4, as assessed by an immunohistochemistry (IHC) assay. The objective of this cohort is to evaluate a range of FPA150 doses to gain additional data on safety, pharmacokinetics (PK) and potential preliminary clinical activity. All patients will undergo pre- and on-treatment biopsies to assess the pharmacodynamic effects of FPA150 on the tumor and the tumor microenvironment.

The Phase 1a dose-escalation portion of FPA150-001 in unselected patients with any solid tumor is currently ongoing. The primary objective of this portion of the trial is to identify a maximum tolerated dose (MTD) or recommended dose (RD) for FPA150 monotherapy.

Once the MTD/RTD has been identified, the company will initiate a Phase 1b dose-expansion portion of the trial in B7-H4 positive tumors, including in breast cancer, ovarian cancer and endometrial cancer. The Phase 1b dose expansion endpoints include objective response rate, as well as safety and PK.

About FPA150

FPA150 is a novel, fully human, afucosylated monoclonal antibody targeting B7-H4. B7-H4 expression is observed in multiple solid tumors, including breast and gynecologic cancers. FPA150 is designed with a dual mechanism of action: blocking the T cell checkpoint activity of B7-H4 as well as delivering ADCC against tumor cells expressing B7-H4.

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 the 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 or follow us on LinkedIn, Twitter and Facebook.

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 (i) the progress and scope of the Phase 1 clinical trial of FPA150; (ii) the potential use of FPA150 to treat patients with cancer; and (iii) the extent of B7-H4 protein expression in patients with cancer. Many factors may cause differences between current expectations and actual results, including unexpected safety or efficacy data observed during non-clinical or clinical studies, clinical site activation rates or clinical trial enrollment rates that are lower than expected and changes in expected or existing competition. 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.

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Last Updated: 19-Oct-2018