Five Prime Therapeutics : Bema P2 Data Presentation KOL Event

A double-blind randomized study of bemarituzumab (bema) plus mFOLFOX6 versus placebo plus mFOLFOX6 as first-line treatment for advanced gastric/gastroesophageal junction cancer (FIGHT)

Zev A Wainberg, MD (David Geffen School of Medicine at UCLA)

January 15, 2021

CONFIDENTIAL © 2021 Five Prime Therapeutics, Inc.

Forward-Looking Statements Disclaimer

This presentation contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "may," "will," "expect," "plan," "anticipate" and similar expressions (as well as other words or expressions referencing future events or circumstances) are intended to identify forward-looking statements. These forward-looking statements reflect Five Prime's current beliefs and expectations. Each of these forward-looking statements involves risks and uncertainties. Actual results may differ from these forward-looking statements. Forward-lookingstatements contained in this presentation include statements about (i) the potential advancement of the development of bemarituzumab; (ii) the potential use of bemarituzumab, including in combination with other products, to treat patients; (iii) the potential development of bemarituzumab in indications in addition to gastric and gastroesophageal cancer; (iv) the timing of the presentation of data for bemarituzumab; and (v) the extent of FGFR2b protein overexpression in certain patient populations. These statements speak only as of the date made and Five Prime is under no obligation and disavows any obligation to update or revise such statements as a result of any event, circumstances or otherwise, unless required by applicable legislation or regulation.

Many factors may cause differences between current expectations and actual results, including unexpected safety or efficacy data observed during preclinical or clinical studies, changes in expected or existing competition, failure of Five Prime's collaborators to support or advance collaborations or product candidates, changes in the regulatory, pricing or reimbursement environment and unexpected litigation or other disputes. In addition, while Five Prime expects the COVID-19 pandemic to adversely affect its business operations and financial results, the extent of the impact on Five Prime's ability to advance its manufacturing, clinical development and regulatory efforts and business and corporate development and other objectives and the value of and market for Five Prime's common stock will depend on future developments that are highly uncertain, and Five Prime cannot predict with confidence the ultimate duration of the pandemic, travel restrictions, quarantines, social distancing and business closure requirements in the U.S. and in other countries and the effectiveness of actions taken globally to contain and treat COVID-19. Other factors that may cause Five Prime's actual results to differ from current expectations are discussed in Five Prime's filings with the U.S. Securities and Exchange Commission, including the "Risk Factors" sections 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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Fibroblast Growth Factor Receptor 2b (FGFR2b) in Cancer

• FGFR2b is a member of the FGFR family (FGFR1-4) and splice isoform of FGFR2
• FGFR2b overexpression: 3-61% of gastric cancer depending on tumor stage and assay1 and has been identified in other cancers of epithelial origin such as squamous cell lung, breast and ovarian cancer2

• FGFR tyrosine kinase inhibitors3 have shown benefit in cancers with FGFR mutations, fusions or translocations

1Han et al, Pathobiology 2015, Ahn et al, Modern Pathology 2016, Nagatsuma et al, Gastric Cancer 2015, Tokunga et al, Oncotarget 2016

2 FivePrime Data on file

3Abou-Alfa GK et al, Lancet Onc 2020; Loriot Y et al, NEJM 2019

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Bemarituzumab is an IgG1 antibody specific for the FGFR2b Receptor

Two Mechanisms of Action:

• Direct inhibition of fibroblast growth factors 7, 10 and 22

Avoids the hyperphosphatemia observed with inhibition of FGF23

• Enhanced antibody dependent cellular cytotoxicity

Bemarituzumab

Bemarituzumab

CONFIDENTIAL © 2021 Five Prime Therapeutics, Inc.	4