Enobosarm Meets Pre-Specified Primary Efficacy Endpoint in Ongoing Phase 2 Clinical Trial in ER+/AR+ Breast Cancer

Demonstration of Clinical Benefit in 9 mg dose cohort achieved
earlier than anticipated

MEMPHIS, Tenn.–(BUSINESS WIRE)–GTx, Inc. (Nasdaq: GTXI) today announced that enobosarm achieved the
pre-specified primary efficacy endpoint in the 9 mg dose cohort from
patients in both stage 1 and the ongoing stage 2 of its Phase 2 clinical
trial in women with advanced, estrogen receptor positive (ER+), androgen
receptor positive (AR+) breast cancer. The primary efficacy endpoint
requires at least nine patients (out of a total of 44 evaluable
patients) to achieve clinical benefit, defined as either a complete
response, partial response or stable disease, as measured by Response
Evaluation Criteria in Solid Tumors (RECIST) at 24 weeks of treatment.
In this ongoing trial, the efficacy endpoint was achieved in the first
22 confirmed evaluable patients, and the trial will continue enrolling
and treating eligible patients with enobosarm until 44 evaluable
patients have completed the trial. Enobosarm has been well tolerated
among patients treated to date in the 9 mg dose cohort with the majority
of adverse events being either grade 1 or 2.

The Company plans to report top-line clinical results from these 22
evaluable patients from the 9 mg dose cohort in December 2016, and
expects to report top-line clinical results from the full study by the
middle of 2017, following completion of the clinical trial.

“Demonstrating success with the 9 mg dose cohort sooner than expected in
22 patients is a significant milestone for the enobosarm program and
GTx, and we look forward to seeing top-line response data in all 44
evaluable patients,” said Robert J. Wills, Ph.D., Executive Chairman of
GTx. “In addition, with these results in hand, we will be discussing how
best to advance the development of enobosarm with potential partners.”

About the Phase 2 Clinical Trial in ER+/AR+ Breast Cancer

The open-label, multi-center, multinational Phase 2 clinical trial
(NCT02463032) will assess the efficacy and safety of orally administered
enobosarm in up to 88 evaluable patients with metastatic or locally
advanced, ER+/AR+ breast cancer. Patients will receive
orally-administered enobosarm (9 mg or 18 mg) daily for up to 24 months.
The two dose cohorts in the trial will be treated independently for the
purpose of assessing efficacy. The first stage of evaluation will be
assessed among the first 18 evaluable patients for each cohort. If at
least 3 of 18 patients achieve clinical benefit at week 24, then the
trial will proceed to the second stage of enrollment for that cohort to
assess clinical benefit in a total of 44 evaluable patients per arm. As
reported in September and November, 2016, respectively, patients in both
the 9 mg and 18 mg cohorts demonstrated sufficient clinical benefit
among the first 18 evaluable patients in each such cohort to advance to
the second and final stage of the clinical trial. Clinical benefit is
defined as a complete response, partial response, or stable disease, as
measured by Response Evaluation Criteria in Solid Tumors (RECIST) at 24
weeks. The lead investigator for the trial is Dr. Beth Overmoyer from
the Dana Farber Cancer Institute and the Harvard Medical School.

About Enobosarm

Enobosarm, a selective androgen receptor modulator (SARM), has been
evaluated in 24 completed or ongoing clinical trials enrolling over
1,500 subjects, of which approximately 1,000 subjects were treated with
enobosarm at doses ranging from 0.1 mg to 100 mg. At all evaluated dose
levels, enobosarm was observed to be generally safe and well tolerated.
Previously, enobosarm 9 mg has been tested in a Phase 2, proof of
concept clinical trial of 22 postmenopausal women with ER+ metastatic
breast cancer who have previously responded to endocrine therapy.
Seventeen of the 22 patients were confirmed to be AR+, and 6 of those 17
patients demonstrated clinical benefit at six months. In total, 7
patients (one patient with indeterminate AR status) achieved clinical
benefit at six months. The results also demonstrated that, after a
median duration on study of 81 days, 41 percent of all patients (9/22)
achieved clinical benefit as best response and also had increased PSA
which appears to be an indicator of AR activity. Enobosarm was well
tolerated. The most common adverse events reported were pain, fatigue,
nausea, hot flash/night sweats, and arthralgia.

About ER+/AR+ Breast Cancer

Breast cancer is the most commonly diagnosed cancer in women, and one in
eight women will develop invasive breast cancer in their lifetime. In
2012, 1.7 million women world-wide were diagnosed with breast cancer,
and there were 6.3 million women alive who had been diagnosed with
breast cancer in the previous five years. Clinical assessment of breast
cancer provides for routine characterization of receptor status,
including the presence or absence of estrogen receptor (ER),
progesterone receptor, and human epidermal growth factor receptor 2
(HER2) in the tumor tissue. Receptor status is used to assess metastatic
potential as well as to guide treatment decisions. The majority of
breast cancers are considered hormone receptor positive (expressing ER
or progesterone receptor). Approximately 70 percent of women in the U.S.
with breast cancer have ER+ tumors, and 75 to 90 percent of these
cancers are also AR+.

Estrogen promotes the growth of breast cancers that are hormone receptor
positive. Therefore, treatment is directed at blocking the effects of
estrogen on the breast cancer either through blocking the estrogen
receptor or minimizing the production of estrogen. This endocrine
therapy is the cornerstone of treatment for the majority of women with
hormone receptor positive advanced breast cancer and is the preferred
initial treatment over alternative approaches such as chemotherapy, due
to its efficacy and favorable safety profile. Patients who respond to
one endocrine therapy are likely to respond to subsequent hormonal
therapies. Therefore, the standard of care for women with hormone
receptor positive breast cancer typically involves the sequencing of
endocrine agents until intolerance or development of resistance occurs,
or metastatic progression necessitates a transition to chemotherapy.
Enobosarm may offer an alternate hormonal approach for the treatment of
endocrine sensitive advanced breast cancer prior to the introduction of
chemotherapy.

About GTx

GTx, Inc., headquartered in Memphis, Tenn., is a biopharmaceutical
company dedicated to the discovery, development and commercialization of
small molecules for the treatment of cancer, including treatments for
breast and prostate cancer, and other serious medical conditions.

Forward-Looking Information is Subject to Risk and Uncertainty

This press release contains forward-looking statements based upon
GTx’s current expectations. Forward-looking statements involve risks and
uncertainties, and include, but are not limited to, statements relating
to the enrollment and conduct of GTx’s ongoing Phase 2 clinical trial of
enobosarm for the treatment of ER+/AR+ breast cancer and the timing
thereof, including the potential therapeutic applications for, and
potential benefits of its SARM (including enobosarm) technology. GTx’s
actual results and the timing of events could differ materially from
those anticipated in such forward-looking statements as a result of
these risks and uncertainties, which include, without limitation, the
risks (i) that if GTx determines to move forward with additional
development of enobosarm for the treatment of ER+/AR+ breast cancer, GTx
will require additional funding, which it may be unable to raise, in
which case, GTx may fail to realize the anticipated benefits from its
SARM technology; (ii) that the clinical trial of enobosarm to treat
ER+/AR+ breast cancer being conducted by GTx may not be completed on
schedule, or at all, or may otherwise be suspended or terminated; (iii)
related to the difficulty and uncertainty of pharmaceutical product
development, including the time and expense required to conduct clinical
trials and analyze data, and the uncertainty of clinical success; and
(iv) related to issues arising during the uncertain and time-consuming
regulatory process, including the risk that GTx may not receive any
approvals to advance the clinical development of one or more potential
clinical SARM candidates. In addition, GTx will continue to need
additional funding and may be unable to raise capital when needed, which
would force GTx to delay, reduce or eliminate its product candidate
development programs and potentially cease operations. GTx’s actual
results and the timing of events could differ materially from those
anticipated in such forward-looking statements as a result of these
risks and uncertainties. You should not place undue reliance on these
forward-looking statements, which apply only as of the date of this
press release. GTx’s quarterly report on Form 10-Q for the period
ending September 30, 2016, contains under the heading, “Risk Factors”, a
more comprehensive description of these and other risks to which GTx is
subject. GTx expressly disclaims any obligation or undertaking to
release publicly any updates or revisions to any forward-looking
statements contained herein to reflect any change in its expectations
with regard thereto or any change in events, conditions or circumstances
on which any such statements are based.

Contacts

Investors:
GTx, Inc.
Lauren Crosby, 901-271-8622
lcrosby@gtxinc.com
or
Media:
Red
House Consulting
Denise Powell, 510-703-9491
denise@redhousecomms.com