Jefferies 2015 Healthcare Conference

Paul J. Hastings Chairman and Chief Executive Officer

June 2, 2015 Safe Harbor Statement

These slides and accompanying oral presentation contain forward-looking statements. All statements, other than statements of historical fact, included in these slides and accompanying oral presentation are forward-looking statements. In some cases, you can identify forward-looking statements by terminology such as “may,” “could,” “will,” “would,” “should,” “expect,” “plan,” “anticipate,” “believe,” “estimate,” “intend,” “predict,” “seek,” “contemplate,” “potential” or “continue” or the negative of these terms or other comparable terminology. Forward-looking statements in these slides and accompanying oral presentation include, but are not limited to, statements about: the initiation, timing, progress and results of our preclinical studies and clinical trials, and our research and development programs; our ability to advance product candidates into, and successfully complete, clinical trials; the tolerability of our product candidates at efficacious doses; our collaborators’ exercise of their license options; the commercialization of our product candidates; the implementation of our business model, strategic plans for our business, product candidates and technology; the scope of protection we are able to establish and maintain for intellectual property rights covering our product candidates and technology; estimates of our expenses, future revenues, capital requirements and our needs for additional financing; the timing or likelihood of regulatory filings and approvals; our ability to maintain and establish collaborations or obtain additional government grant funding; our financial performance; and developments relating to our competitors and our industry.

These statements relate to future events or to our future financial performance and involve known and unknown risks, uncertainties and other factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by these forward-looking statements. Such risks and uncertainties include, among others, the uncertainties inherent in the preclinical and clinical development process; the risks and uncertainties of the regulatory approval process; our dependence on our collaboration partners, including Celgene, GlaxoSmithKline and Bayer, for the funding of our partnered programs; our ability to raise additional capital to support the development of our unpartnered programs; our dependence on the development and marketing efforts of our partners for the commercial success of our partnered product candidates; our reliance on third parties to conduct certain preclinical studies and all of our clinical trials; our reliance on single source third-party contract manufacturing organizations to manufacture and supply our product candidates; our ability to validate, develop and obtain regulatory approval for companion diagnostics; our ability to achieve market acceptance and commercial success of our product candidates once regulatory approval is achieved; our ability to discover, develop and commercialize additional product candidates; the ability of competitors to discover, develop or commercialize competing products more quickly or more successfully; our dependence on our Chairman and Chief Executive Officer, our Chief Scientific Officer, our Chief Medical Officer and other key executives; risk of third party claims alleging infringement of patents and proprietary rights or seeking to invalidate our patents or proprietary rights; and the ability of our proprietary rights to protect our technologies and product candidates. Other factors that may cause actual results to differ materially from current expectations include, among other things, those listed under “Risk Factors” or otherwise described in our Annual Report on Form 10-K for the fiscal year ended December 31, 2014, filed with the Securities and Exchange Commission (SEC) on March 12, 2015 and our Quarterly Report on Form 10-Q for the fiscal quarter ended March 31, 2015, filed with the SEC on May 7, 2015.

Any forward-looking statement you see or hear during this presentation reflects our current views with respect to future events and is subject to these and other risks, uncertainties and assumptions relating to our operations, results of operations, industry and future growth. Given these uncertainties, you should not place undue reliance on these forward-looking statements. Except as required by law, we assume no obligation to update or revise these forward- looking statements for any reason, even if new information becomes available in the future.

2 OncoMed Pharmaceuticals, Inc.

• Targeting critical cancer stem cell and immuno-oncology Proprietary pathways Discovery • Pipeline of first-in-class anti-cancer stem cell therapeutics Capabilities • All discovered at OncoMed

• 6 clinical programs in or advancing to Phase 2 Deep − 7th program IND filed Clinical Pipeline • 16 active clinical trials: evidence of activity • Data from multiple randomized Phase 2 trials by 2016-17

Strong • Partnerships with Celgene, Bayer and GSK Long-Term • Ongoing discovery research fueling pipeline Outlook • Substantial future milestones and cash

3 Cancer Stem Cells Drive Tumor Growth, Recurrence and Metastasis

CSCs Drive Tumor Growth Anti-CSC Therapy Blocks Renewal; Forces Differentiation Human CSCs

colon tumor CD44

CD166 Self-renewal

) CSC (7/8) Other (0/10) Human colon tumor growth

in mouse xenograft Tumor Volume(mm3 Tumor

Day post-injection Differentiation

FACS analysis of CSCs

human tumor in mouse CD44

CD166 4 Targeting Critical Stem Cell Pathways

Notch Wnt RSPO/LGR New Pathway Pathway Pathway Pathways

• Demcizumab • Vantictumab • Anti-RSPO3 • Immunotherapy • Tarextumab • Ipafricept • Other RSPOs • Hippo • Brontictuzumab • Small • Other LGRs • Undisclosed Molecules • Anti-DLL4/VEGF bispecific

5 Anti-Cancer Stem Cell Pipeline 6 Clinical Programs, 5+ Research Programs

Therapeutic Preclinical IND Phase 1a Phase 1b Phase 2

Demcizumab Anti-DLL4; OMP-21M18

Tarextumab Anti-Notch2/3; OMP-59R5 Vantictumab anti-Fzd7, OMP-18R5 Ipafricept

Fzd8-Fc; OMP-54F28 CLINICAL Brontictuzumab Anti-Notch1; OMP-52M51 Anti-DLL4/VEGF OMP-305B83

Anti-RSPO3 Filed OMP-131R10 Small Molecules WNT inhibitors

Immunotherapy

PRECLINICAL Hippo Pathway Small Molecules (Undisclosed) 6 Demcizumab (anti-DLL4) Inhibits Tumor Growth by Three Distinct Mechanisms

Blocking DLL4 function reduces CSC, inhibits tumor angiogenesis and relieves immune suppression

Cancer Stem Cells Angiogenesis Immune Response

Promotes Blocks critical DLL4 Reduced IL-17 production differentiation and role in angiogenesis Reduced monocytic chemo sensitization myeloid-derived suppressor cells (MDSCs)

7 Demcizumab Clinical Program

Single agent Combo with chemo Randomized

Phase 2 Phase 1b Enrolling Pancreatic Cancer YOSEMITE Pancreatic Cancer Phase 1a Phase 1b Advanced solid Phase 2 Non-Small Cell DENALI Enrolling tumors Lung NSCLC

Phase 1b/2 Currently Ovarian In Ph1b

• Multi-pronged MOA • Single agent activity observed – partial and minor responses • Generally well tolerated − Truncated dosing mitigates cardiopulmonary toxicity

8 Demcizumab Phase 1b Pancreatic Cancer Response Rates

First-line Pancreatic Cancer (N=29)

Demcizumab + Gemcitabine + Abraxane % Change in Tumor Size in % Change Tumor

89% Overall Clinical Benefit Rate Demcizumab + Abraxane + Abraxane + Gemcitabine* (N=29) Gemcitabine** Partial Response 14 (50%) 23% Stable Disease 11 (39%) 27%

Hidalgo, et al ASCO 2015 * Single arm study, unconfirmed responses **MPACT Phase 3 study; Von Hoff, et al, NEJM 2013 9 Demcizumab Phase 1b Pancreatic Cancer Duration of Responses

Progression-free Survival Overall Survival Demcizumab + Abraxane + Gemcitabine Demcizumab + Abraxane + Gemcitabine

mPFS (95% CI) = 9.0 months (3.7– NR) mOS (95% CI) = 10.1 months (6.5 – 16.2)

Probability Probability

0 5 10 15 0 5 10 15 Months Months Survival Rates Demcizumab + Abraxane + Abraxane + Gemcitabine* Gemcitabine** Progression-free Survival 9.0 months 5.5 months Overall Survival 10.1 months 8.5 months

Hidalgo, et al ASCO 2015 *Single arm study, unconfirmed responses **MPACT Phase 3 study; Von Hoff, et al, NEJM 2013 10 Demcizumab Phase 1b NSCLC Response Rates

First-Line Advanced NSCLC (N=40)

Demcizumab + Pemetrexed + Carboplatin % Change in Tumor Size in % Change Tumor

89% Overall Clinical Benefit Rate Demcizumab + Pemetrexed Pemetrexed + + Carboplatin (N=40)* Carboplatin** Complete Response 1 (3%) Partial Response 19 (48%) 27% Stable Disease 15 (38%) Kotasek, et al ASCO 2015 * Single arm study, unconfirmed responses ** Alimta® (pemetrexed) Package insert 11 NSCLC Overall Survival by Kaplan Meier Phase 1b Exploratory Analysis

Truncated Demcizumab Dosing Continuous Demcizumab Dosing “Worst Case” Survival Analysis mOS (95% CI) = 8.1 (5.8-NR) mos

mOS (95% CI) = 6.3 months (3.2-NR) % Alive %

0 5 10 Months 15 20 25 % Alive % Tumor Biomarker Analysis (%Tils)

% %TILsTILs >50% >50%

0 10 20 30 40 50 Months %TILs ≤50% Ten of 23 patients (~40%) alive >2 years Survival Overall %TILs ≤50%

Kotasek, ASCO 2015 Survival days 12 Tarextumab: Anti-Notch2/3 Antibody

Single agent Combo with chemo Randomized Phase 1b/2 ALPINEPhase Study 1b/2 PancreaticALPINE Cancer Enrolling Pancreatic Phase 1a Phase 1b/2 Advanced solid tumors PINNACLEPhase Study 1b/2 Small CellPINNACLE Lung Cancer Enrolling Small Cell Lung Cancer

• Reduces CSCs; promotes differentiation • Single agent activity On-target, manageable GI toxicities • Predictive biomarker program − Notch3+ tumor status

13 Tarextumab Phase 1b ALPINE Response Rates

First-line Pancreatic Cancer (N=37) Tarextumab + Abraxane + Gemcitabine

= Tarextumab + Gemcitabine = Tarextumab + Gemcitabine + Abraxane

30% target tumor reduction % Change in Tumor Size Tumor in Change%

73% Overall Clinical Benefit Rate Tarextumab + Abraxan+ Gemcitabinee* (N=24) Abraxane + Gemcitabine** Partial Response 11 (38%) 23% Stable Disease 10 (35%) 27% PR + SD 21 (73%) 50%

O’Reilly, et al ASCO GI 2015 *Single arm study, unconfirmed responses **MPACT Phase 3 study; Von Hoff, et al, NEJM 2013 14 Tarextumab Phase 1b ALPINE Duration and Biomarker Data

Tumor Notch3 Level and Timed Endpoints

14.6months

Progression-free Survival and Overall Survival Tarextumab + Gemcitabine + mPFS (months) mOS (months) Abraxane* All patients (N=24) 5.6 11.6 Notch3 high (50%) (N=12) 6.6 14.6 Gemcitabine + Abraxane** 5.5 8.5

O’Reilly, et al ASCO GI 2015 *Single arm study, unconfirmed responses **MPACT Phase 3 study; Von Hoff, et al, NEJM 2013 15 Tarextumab Phase 1b PINNACLE Response Rates

Extensive-stage SCLC (N=26)

Tarextumab + Etoposide + Cisplatin/Carboplatin % Change in Tumor Size in % Change Tumor

100% Overall Clinical Benefit Rate (N=26) Tarextumab + Cisplatin + Etoposide + Etoposide** Carboplatin/Cisplatin Partial Response 20 (77%) 44%-67% Stable Disease 6 (23%)

Pietanza, et al ASCO 2015 * Single arm study, unconfirmed responses **SCLC Meta-Analysis; Rossi, et al, JCO 2012 16 Tarextumab Phase 1b PINNACLE Biomarker and Survival Analysis

Progression-Free Survival Overall Survival Low Notch3 vs. High Notch3 Low Notch3 vs. High Notch3

Low Notch 3 High Notch 3 Low Notch 3 High NotchN=13 3 N=12 N=13 N=12 N=13

Months Months Months Months

Potentially longer survival noted in Notch3 high patients receiving higher doses of tarextumab (≥12.5mg/kg) + platinum therapy

Pietanza, et al ASCO 2015 17 Brontictuzumab: Anti-Notch1 Antibody

Dose Escalation Expansion Cohort

Phase 1a Phase 1a Ongoing Advanced solid tumors Biomarker selected expansion

Phase 1a Phase 1a Hematologic Ongoing malignancies Biomarker selected dose escalation

• Anti-CSC, anti-angiogenic • Single agent activity On-target, manageable GI toxicities • Predictive biomarker program − IHC assay identifying solid tumors with Notch1 activation

18 Brontictuzumab Phase 1a Solid Tumor Trial with Biomarker Assay

Responses among Evaluable Subjects (N=17) Phase 1a Expansion Notch1 High Notch1 Low Notch1 ? Now Enrolling Partial Response 1 - - Solid Tumor Types with Notch1 ICD High Stable Disease Prevalence (12%-53%) 2 1 • Colorectal Progressive Disease 1 8 4 • Gastric • Esophageal Total 4 9 4 • Pancreatic • Small cell lung Predictive Biomarker (Notch1) • HER2- breast • 3 of 4 patients with Notch1 ICD high • Cholangiocarcinoma tumors with clinical benefit • Adenoid cystic carcinoma • 1 of 9 patients with Notch1 ICD low tumors with clinical benefit

Patnaik, et al EORTC-NCI-AACR 2014 19 Vantictumab (anti-Fzd7) WNT Pathway

Single agent Combo with chemo

Phase 1b Her2- Breast Cancer paclitaxel

Phase 1a Phase 1b Advanced solid tumors NSCLC docetaxel Phase 1b Pancreatic Cancer gemcitabine + Abraxane

• Inhibits Wnt signaling − Blocks Frizzled 1, 2, 5, 7, 8 • On-target, mild-to-moderate bone-related AEs observed − Bone protection strategy • Single agent activity 3/3 neuroendocrine tumors

20 Ipafricept (Fzd8-FC) WNT Pathway

Single agent Combo with chemo

Phase 1b Ovarian carboplatin + paclitaxel

Phase 1a Phase 1b Advanced solid tumors Hepatocellular sorafenib

Phase 1b Pancreatic gemcitabine + Abraxane

• Inhibits signaling: binds Wnt ligands − Distinct from vantictumab • On-target, mild-to-moderate bone-related AEs observed − Bone protection strategy • Single agent activity in diverse tumor types; SD > 112 days in 9 patients

21 Anti-DLL4/VEGF Bispecific (OMP-305B83)

Single agent

Phase 1a Advanced solid tumors Anti- VEGF Anti-DLL4 Heavy chain Heavy chain

• Dual inhibitor DLL4 & VEGF • Multi-pronged MOA • Preclinical data: improved efficacy and safety • Phase 1a initiated December 2014 − Dose escalation, expansion − Advanced, refractory solid tumors

Yen AACR 2014 22 New R&D Candidates

Anti-RSPO3 (OMP-131R10) Immuno-oncology Two novel immuno-oncology IND filed April 2015 • • programs • Multiple therapeutic opportunities – Hippo pathway (Celgene) – Strong predictive biomarker strategy – GITR Ligand-Fc (OMED wholly owned) • Broad, issued claims cover therapeutic antibodies that disrupt RSPO-LGR signaling GITRL-Fc

RSPO LGR • Discovery of “missing” checkpoint receptor to PD-L2 – OMED wholly owned

Other Anti-RSPO candidates • RSPO 1, 2, 4; LGR 4, 5, 6

Gurney AACR 2014

23 3 Significant Partnerships Provide Funding and Value

Partner Year Upfront Comments • Up to 6 biologics + small molecules • Co-development/commercialization on 5 of 6 biologics – Demcizumab end of Phase 2 opt-in – Anti-DLL4/VEGF, RSPO3, others Phase 1 opt-in 2013 $177M* – 1/3 OMED – 2/3 CELG development cost share – 50-50 US profit share – Ex-US royalties • Celgene equity stake ~5% • Up to 3 biologic & 2 small molecule programs • Opt-in through end of Phase 1b for vantictumab, 2010 $40M ipafricept • Mid-single digit to high teens royalties on biologics • 2 biologics programs • Opt-in at end of Phase 2 for tarextumab 2007, $35M* • Opt-in at end of Phase 1 or Phase 2 for brontictuzumab 2011 • Low double-digit to high teens royalties • GSK equity stake ~8.8%

*Celgene: $155M cash, $22.25 equity; GSK: $17.5M cash, $17.5M equity Note: equity % stake per most recent SEC filing 24 Program Financial Milestone Snapshot

Program Potential Future Milestones/Payments Demcizumab ~$790M Tarextumab $319.5M Vantictumab $357.5M Ipafricept $347.5M Brontictuzumab $330.5M Anti-DLL4/VEGF bispecific ~$505M Anti-RSPO3 ~$440M RSPO/undisclosed pathway ~$440M each, up to 3 Bayer small molecules $110M Celgene small molecules >$100M Total Potential Milestones >$4 Billion

Over $378M* received to date from Celgene, Bayer, GSK

*Includes $5M receivable 25 Potential Collaborative Revenue 2015-16

Milestone/Payments Partner Amount Timing

Brontictuzumab Phase 1 $5M 1H 2015 expansion Demcizumab Phase 2 safety $70M Q4 2015/2016 analysis

Vantictumab opt-in $25M 2H 2015/2016

Ipafricept opt-in $15M 2H 2015/2016

2H 2015/2016 Brontictuzumab opt-in $18.75M Payment increases to $25M if GSK chooses to wait to opt in at Phase 2

Tarextumab opt-in $25M 2016

Total Potential Milestones >$150M Through 1H 2016*

* Additional milestones could be achieved in 2015/2016 related to preclinical and small molecule programs

26 OMED Financial Guidance

• Cash*: $213M as of March 31, 2015

• 2015 Financial Guidance: – $100 - $110M cash operating expenses, excluding non-cash expenses – YE cash of over $120M before potential milestone payments • $150M+ in potential 2015/16 payments from existing partnerships • Existing cash plus future milestones may fund operations through commercialization without need for future financing

* Cash, equivalents, and short-term investments; unaudited 27 2015 Pipeline Progress

1H 2015 2H 2015  Anti-DLL4/VEGF Phase 1a FPI Complete Demcizumab Phase 1b Ovarian  ASCO GI - Tarextumab Final Phase 1b pancreatic; biomarker Anti-RSPO3 Phase 1a FPI  Phase1a Brontictuzumab expansion Complete Tarextumab Phase 2  Demcizumab NSCLC Phase 2 FPI enrollment in pancreatic cancer  Demcizumab Pancreatic Phase 2 FPI Present Phase 1a Brontictuzumab data Biomarker-selected expansion cohort  ELCC - Demcizumab Updated Phase 1b NSCLC data Present Ipafricept data AACR  7 abstracts accepted for presentation Present Vantictumab data R&D Investor Day  April 29 in NYC Present opt-in package to Bayer  File anti-RSPO3 IND Vantictumab & ipafricept 2015 / 2016 ASCO - Tarextumab Demcizumab Phase 2 safety analysis  Phase 1b SCLC  ASCO - Demcizumab Phase 1b Pancreatic & NSCLC Financial/Corporate* Data Clinical

* Select financial milestones 28 OncoMed Pharmaceuticals, Inc.

• Targeting critical cancer stem cell and immuno-oncology Proprietary pathways Discovery • Pipeline of first-in-class anti-cancer stem cell therapeutics Capabilities • All discovered at OncoMed

• 6 clinical programs in or advancing to Phase 2 Deep − 7th program IND filed Clinical Pipeline • 16 active clinical trials: evidence of activity • Data from multiple randomized Phase 2 trials by 2016-17

Strong • Partnerships with Celgene, Bayer and GSK Long-Term • Ongoing discovery research fueling pipeline Outlook • Substantial future milestones and cash

29 Thank you