Epizyme Reports Updated Data from Phase 2 Trial of Tazemetostat for Epithelioid Sarcoma at 2019 ASCO Annual Meeting

New Clinical Data Presented Today Included in Recently Submitted NDA
to FDA

CAMBRIDGE, Mass.–(BUSINESS WIRE)–Epizyme,
Inc. (Nasdaq: EPZM), a late-stage biopharmaceutical company
developing novel epigenetic therapies, today reported updated data on
tazemetostat from the epithelioid sarcoma cohort of its ongoing Phase 2
study in patients with molecularly defined solid tumors. The data will
be presented today in an oral
presentation entitled “Safety and efficacy of tazemetostat, a
first-in-class EZH2 inhibitor, in patients with epithelioid sarcoma” at
the 2019 American Society of Clinical Oncology (ASCO) Annual Meeting by
Silvia Stacchiotti, M.D., Fondazione IRCCS Istituto Nazionale Tumori,
Milan, and an investigator in the Phase 2 clinical trial.

In July 2017, Epizyme completed enrollment of 62 patients in the
epithelioid sarcoma cohort of its Phase 2 trial. Updated data reported
today from that cohort are as of a September 17, 2018 cutoff date.
Findings include that treatment with tazemetostat resulted in a 15%
objective response rate (ORR) and a 26% disease control rate (DCR). The
median duration of response (DOR) has not yet been reached. Among the 62
patients, tazemetostat continues to be generally well-tolerated with
favorable safety.

“Today, there are limited effective and tolerable treatment options
available for patients with epithelioid sarcoma, a rare and aggressive
cancer that affects people in the prime of their lives,” said Dr.
Shefali Agarwal, chief medical officer of Epizyme. “We are pleased that
the data presented today are consistent with what we have seen
throughout our development of tazemetostat for epithelioid sarcoma,
demonstrating meaningful clinical activity and good tolerability.
Importantly, the totality of these data formed the foundation for our
first NDA submission, which we just announced last week. If we are
successful, tazemetostat would be the first FDA-approved EZH2 inhibitor.
We are thankful to the patients, physicians and caregivers who have
participated in our study and hope that tazemetostat may positively
impact patients with this devastating cancer in the future.”

Efficacy Data
The epithelioid sarcoma cohort in Epizyme’s
Phase 2 study represents the largest prospective study of epithelioid
sarcoma with any approved or investigational anticancer treatment to
date. Epithelioid sarcoma is an ultra-rare and aggressive soft tissue
sarcoma, characterized by a loss of the INI1 protein. It is most
commonly diagnosed in young adults (20-40 years old) and is often fatal,
with a median overall survival (OS) of less than one year in patients
with metastatic disease.

The fully enrolled cohort includes 24 treatment-naive patients and 38
relapsed and/or refractory patients for a total of 62 adult and
pediatric epithelioid sarcoma patients (at least 16 years of age).
Patients enrolled were administered 800 mg of tazemetostat orally twice
daily. The primary endpoint of the study is ORR, comprised of complete
and partial responses as measured by RECIST 1.1. Secondary endpoints
include DOR, DCR, OS and safety.

Updated findings are summarized below, based on a September 17, 2018
data cut-off date.

*Comprised of confirmed objective responses for any duration or disease
stabilization of 32 weeks or more

Tazemetostat Safety Data
Favorable safety and tolerability
have been observed with tazemetostat in this Phase 2 study cohort. The
majority of treatment-emergent adverse events (TEAEs) were grade 1 or 2,
with only 13 percent of patients experiencing grade 3 or higher
treatment-related TEAEs. Reported TEAEs regardless of attribution with
an incidence of 10% or greater were fatigue (39%), nausea (35%), cancer
pain (32%), decreased appetite (26%), constipation (21%), vomiting
(24%), cough and headache (18% each), diarrhea, weight decrease and
anemia (16% each), dyspnea (13%) and plural effusion (11.% ). Two
percent of patients were dose-reduced due to an adverse event and one
patient discontinued treatment due to an adverse event in the Phase 2
cohort.

The safety data from the 62 epithelioid sarcoma patients in the study
cohort are consistent with the overall safety observed to date in over
800 people in the tazemetostat clinical program.

Tazemetostat NDA Submission for Epithelioid Sarcoma
In May,
Epizyme announced that it submitted the New Drug Application (NDA) for
tazemetostat for the treatment of patients with metastatic or locally
advanced epithelioid sarcoma not eligible for curative surgery to the
US. Food and Drug Administration (FDA). The FDA has a 60-day filing
review period to determine whether the NDA is complete and acceptable
for filing.

About Epithelioid Sarcoma
Epithelioid sarcoma is an
ultra-rare soft tissue sarcoma characterized by a loss of the protein
INI1. Patients are most commonly diagnosed as young adults, between 20
and 40 years of age. Median overall survival from initial diagnosis is
30 months. Epithelioid sarcoma becomes more aggressive after recurrence
or metastases, with a typical survival of less than one year for
patients with metastatic disease.

About the Tazemetostat Clinical Trial Program
Tazemetostat,
an oral, potent, first-in-class EZH2 inhibitor, is currently being
studied as a monotherapy in ongoing clinical programs in patients with
certain molecularly defined solid tumors, including epithelioid sarcoma
and other INI1-negative tumors, and in patients with follicular
lymphoma, both with and without EZH2 activating mutations. Multiple
clinical studies are underway through collaborations assessing
tazemetostat as a combination treatment for patients with diffuse large
B-cell lymphoma. Epizyme also plans to conduct multiple additional
clinical trials designed to evaluate the potential benefit of
tazemetostat in earlier lines of therapy for follicular lymphoma, as
well as new combinations and cancer indications.

About Epizyme, Inc.
Epizyme, Inc. is a late-stage
biopharmaceutical company committed to rewriting treatment for cancer
and other serious diseases through novel epigenetic medicines. Epizyme
is broadly developing its lead product candidate, tazemetostat, a
first-in-class EZH2 inhibitor, with studies underway in both solid
tumors and hematological malignancies, as a monotherapy and combination
therapy in relapsed and front-line disease. The company also is
developing a novel G9a program with its next development candidate,
EZM8266, which is targeting sickle cell disease. By focusing on the
genetic drivers of disease, Epizyme’s science seeks to match targeted
medicines with the patients who need them. For more information, visit www.epizyme.com.

Cautionary Note on Forward-Looking Statements
Any statements
in this press release about future expectations, plans and prospects for
Epizyme, Inc. and other statements containing the words “anticipate,”
“believe,” “estimate,” “expect,” “intend,” “may,” “plan,” “predict,”
“project,” “target,” “potential,” “will,” “would,” “could,” “should,”
“continue,” and similar expressions, constitute forward-looking
statements within the meaning of The Private Securities Litigation
Reform Act of 1995. Actual results may differ materially from those
indicated by such forward-looking statements as a result of various
important factors, including: uncertainties inherent in the initiation
of future clinical studies and in the availability and timing of data
from ongoing clinical studies; whether interim results from a clinical
trial will be predictive of the final results of the trial; whether
results from preclinical studies or earlier clinical studies will be
predictive of the results of future trials; whether results from
clinical studies will warrant meetings with regulatory authorities,
submissions for regulatory approval or review by governmental
authorities under the accelerated approval process; whether Fast Track
Designation and Orphan Drug Designations will provide the benefits for
which tazemetostat is eligible; expectations for regulatory approvals,
including accelerated approval, to conduct trials or to market products;
whether the company’s cash resources will be sufficient to fund the
company’s foreseeable and unforeseeable operating expenses and capital
expenditure requirements; other matters that could affect the
availability or commercial potential of the company’s therapeutic
candidates; and other factors discussed in the “Risk Factors” section of
the company’s most recent Form 10-Q filed with the SEC and in the
company’s other filings from time to time with the SEC. In addition, the
forward-looking statements included in this press release represent the
company’s views as of the date hereof and should not be relied upon as
representing the company’s views as of any date subsequent to the date
hereof. The company anticipates that subsequent events and developments
will cause the company’s views to change. However, while the company may
elect to update these forward-looking statements at some point in the
future, the company specifically disclaims any obligation to do so.

Contacts

Media:
Erin Graves, Epizyme, Inc.
[email protected]
(617)
500-0615

Investors:
Chelcie Lister, THRUST Strategic Communications
[email protected]
(919)
777-3049