OncoMed Pharmaceuticals Initiates First Phase 1b Clinical Trial of First-in-Class WNT-Pathway-Targeting Antibody Vantictumab

OncoMed Pharmaceuticals Initiates First Phase 1b Clinical Trial of
First-in-Class WNT-Pathway-Targeting Antibody Vantictumab (OMP-18R5) With
Paclitaxel in Breast Cancer

REDWOOD CITY, Calif., Oct. 29, 2013 (GLOBE NEWSWIRE) -- OncoMed
Pharmaceuticals, Inc. (Nasdaq:OMED), a clinical-stage company developing novel
therapeutics that target cancer stem cells (CSCs), or tumor-initiating cells,
today announced that it has started a multi-center Phase 1b clinical trial of
its first-in-class Wnt-pathway-targeting antibody vantictumab (OMP-18R5) with
paclitaxel in breast cancer. This trial is the first of three Phase 1b trials
for vantictumab that OncoMed expects to initiate this year as part of
OncoMed's collaboration with Bayer Pharma AG.Interim results for the
single-agent first-in-human Phase 1a trial for vantictumab in solid tumor
patients were recently reported at the 2013 European Cancer Congress (ECC
2013) in Amsterdam, NL in September 2013. Additionally, vantictumab clinical
biomarker data from the Phase 1a trial were presented at the AACR-NCI-EORTC
International Conference on Molecular Targets and Cancer Therapeutics in
Boston, MA in October 2013.

The Phase 1b clinical trial is a dose escalation study of the anti-CSC
antibody vantictumab in combination with paclitaxel in patients with first-,
second- and third-line, locally advanced or metastatic HER2 negative breast
cancer. Primary objectives of the trial are to evaluate safety of this
combination regimen and determine a recommended Phase 2 dose for vantictumab
in combination with paclitaxel. Key secondary and exploratory objectives
include evaluation of the pharmacokinetics (PK) of vantictumab, as well as the
pharmacodynamics (PD) and efficacy of this combination. Tumor tissue from
patients will be used to explore predictive biomarker hypotheses related to
the efficacy of vantictumab.

Dr. Carlos Becerra at the Baylor Sammons Cancer Center – The US Oncology
Network, Dallas, TX, is the Principal Investigator who treated the first
patient enrolled in this study and noted, "Breast cancer patients with
advanced HER2 negative disease are in need of novel agents that have a lasting
impact on their cancer.Vantictumab has the potential to have an impact for
breast cancer patients in combination with standard paclitaxel chemotherapy
because of its novel mechanism of action targeting cancer stem cells."

The other investigators and clinical sites to participate in the trial are Dr.
Donald Richards at The US Oncology Network, Tyler, TX, and Dr. Monica Mita at
the Cedars-SinaiMedical Center in Los Angeles, CA.

Dr. Jakob Dupont, Chief Medical Officer of OncoMed, commented, "The Wnt
pathway has been an area of interest for breast cancer researchers for many
years, and it is exciting to bring this novel Wnt targeting antibody,
vantictumab, to the clinic to learn more about the safety and potential
efficacy of the drug candidate in combination with paclitaxel in patients with
advanced HER2 negative breast cancer."

Paul Hastings, Chairman and Chief Executive Officer of OncoMed, noted,
"Initiation of the Phase 1b portion of the vantictumab clinical development
program is an important milestone for OncoMed and for our partnership with
Bayer.The clinical data from this and two other Phase 1b trials with
vantictumab could potentially lead to an opt-in decision by Bayer to take
vantictumab into later stage randomized clinical trials."

About Vantictumab (OMP-18R5)

Vantictumab is a first-in-class antibody that has shown broad anti-CSC and
anti-tumor activity in patient-derived xenograft tumor models.Vantictumab
inhibits a key signaling pathway in cancer, the Wnt pathway.Specifically,
vantictumab selectively targets Frizzled receptors, which are activators of
Wnt signaling.Although vantictumab was originally identified by binding to
Frizzled7, the antibody selectively targets five different Frizzled
receptors.Vantictumab is currently in Phase 1a.Data from this clinical trial
were presented at the European Cancer Conference (ECC 2013) in September 2013
in Amsterdam, NL. Biomarker data for this Phase 1a trial were presented at the
AACR-NCI-EORTC International Conference on Molecular Targets and Cancer
Therapeutics in Boston, MA, in October 2013. Vantictumab is now being tested
in combination with standard-of care-chemotherapy in a Phase 1b clinical trial
in advanced HER2 negative Breast Cancer (vantictumab + paclitaxel).Two
additional Phase1b trials are planned to start in 2013 with vantictumab in
combination with standard-of-care chemotherapy in two distinct solid tumor
indications.Vantictumab is part of OncoMed's collaboration with Bayer Pharma

About Cancer Stem Cells

Cancer stem cells, or CSCs, are the subpopulation of cells in a tumor
responsible for driving growth and metastasis of the tumor.CSCs, also known
as tumor-initiating cells, exhibit certain properties which include the
capacity to divide and give rise to new CSCs via a process called self-renewal
and the capacity to differentiate or change into the other cells that form the
bulk of the tumor.Common cancer drugs target bulk tumor cells but have
limited impact on CSCs, thereby providing a path for recurrence of the
tumor.OncoMed's product candidates target CSCs by blocking self-renewal and
driving differentiation of CSCs toward a non-tumorigenic state, and also
impact bulk tumor cells.OncoMed believes its product candidates are distinct
from the current generations of chemotherapies and targeted therapies, and
have the potential to significantly impact cancer treatment and the clinical
outcome of patients with cancer.

About OncoMed Pharmaceuticals

OncoMed Pharmaceuticals, Inc., is a clinical-stage company focused on
discovering and developing novel therapeutics targeting cancer stem cells
(CSCs).OncoMed has five anti-cancer product candidates in clinical
development, including demcizumab (Anti-DLL4, OMP-21M18), OMP-59R5
(Anti-Notch2/3), OMP-52M51 (Anti-Notch1), vantictumab (Anti-Fzd7, OMP-18R5),
and OMP-54F28 (Fzd8-Fc), which target key CSC signaling pathways including
Notch and Wnt.OncoMed has two other antibodies in preclinical development
with Investigational New Drug filings planned as early as 2014.OncoMed is
also pursuing discovery of additional novel anti-CSC product
candidates.OncoMed has formed strategic alliances with Bayer Pharma AG and
GlaxoSmithKline (GSK). Additional information can be found at the company's
website: www.oncomed.com.

Forward-Looking Statements

To the extent that statements contained in this press release are not
descriptions of historical facts regarding OncoMed Pharmaceuticals, they are
forward-looking statements reflecting the current beliefs and expectations of
management made pursuant to the safe harbor provisions of the Private
Securities Litigation Reform Act of 1995, including OncoMed's expectations
regarding the success of Phase 1b trials for vantictumab and the potential for
an opt-in decision by Bayer; the potential of vantictumab to improve patient
outcomes, particularly in breast cancer patients; the potential for
development of predictive biomarkers for vantictumab, especially in breast
cancer; the potential of OncoMed's product candidates to significantly impact
cancer treatment and the clinical outcome of patients with cancer; and the
timing of Investigational New Drug filings and clinical trials. Such
forward-looking statements involve substantial risks and uncertainties that
could cause OncoMed's clinical development programs, future results,
performance or achievements to differ significantly from those expressed or
implied by the 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; OncoMed's dependence on its collaboration partners,
including GSK and Bayer, for the funding of its partnered programs; OncoMed's
ability to raise capital to support the development of its unpartnered
programs; OncoMed's dependence on the development and marketing efforts of its
partners for the commercial success of its partnered product candidates;
OncoMed's reliance on third parties to conduct certain preclinical studies and
all of its clinical trials; OncoMed's reliance on single source third-party
contract manufacturing organizations to manufacture and supply its product
candidates; OncoMed's ability to validate, develop and obtain regulatory
approval for companion diagnostics; OncoMed's ability to achieve market
acceptance and commercial success of its product candidates once regulatory
approval is achieved; OncoMed's 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;
OncoMed's dependence on its Chairman and Chief Executive Officer, its Chief
Scientific Officer, its Chief Medical Officer and other key executives; risk
of third party claims alleging infringement of patents and proprietary rights
or seeking to invalidate OncoMed's patents or proprietary rights; and the
ability of OncoMed's proprietary rights to protect its technologies and
product candidates. OncoMed undertakes no obligation to update or revise any
forward-looking statements. For a further description of the risks and
uncertainties that could cause actual results to differ from those expressed
in these forward-looking statements, as well as risks relating to OncoMed's
business in general, see OncoMed's Prospectus filed with the Securities and
Exchange Commission on July 18, 2013 and OncoMed's Quarterly Report on Form
10-Q for the fiscal quarter ended June 30, 2013, filed with the Securities and
Exchange Commission on September 3, 2013.

CONTACT: Investor Contact:
         OncoMed Pharmaceuticals
         Shari Annes
         Investor Relations
         (650) 888-0902
         Media Inquiries:
         BCC Partners
         Karen L. Bergman or
         Michelle Corral
         (650) 575-1509 or (415) 794-8662
         kbergman@bccpartners.com or

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