GTx Reports Results from Ongoing Enobosarm Phase 2 Clinical Trial in ER+/AR+ Breast Cancer

– Primary efficacy endpoint met in the enobosarm 9 mg cohort –

– To date, of 22 evaluable patients, 2 had a partial response and 7
had stable disease at 24 weeks –

– Current mean duration of response is 31 weeks, with 7 of 9
responders still receiving enobosarm –

MEMPHIS, Tenn.–(BUSINESS WIRE)–GTx, Inc. (Nasdaq: GTXI) announced today positive initial data from its
ongoing open-label enobosarm Phase 2 clinical trial in women with
advanced, estrogen receptor positive (ER+), androgen receptor positive
(AR+) breast cancer. The pre-specified threshold for success of the
trial was met early in the 9 mg cohort with 9 patients achieving a
clinical benefit response at 24 weeks among the first 22 evaluable
patients in that cohort, as reported by the Company on November 28,
2016. Clinical Benefit Response (CBR) is defined as a complete response
(CR), partial response (PR) or stable disease (SD), as measured by
Response Evaluation Criteria in Solid Tumors (RECIST) at 24 weeks of
treatment.

For the 9 patients achieving CBR in the 9 mg cohort, the results are as
follows:

  • 2 patients demonstrated a PR with a mean reduction in tumor size of
    44.4% from baseline;
  • 7 patients exhibited SD; and of these patients:

    • 3 patients had measurable disease with an average reduction in
      tumor size from baseline of approximately 13%. One of these 3
      patients, whose tumor size was reduced by 25% from baseline at 24
      weeks, had demonstrated a PR (≥ 30% reduction) at 12 weeks.
    • 4 patients with SD had bone-only disease, which made them
      unevaluable for PR.
  • The mean duration of response at the time of the Company’s November
    28, 2016 announcement for the 9 responders was 31 weeks, with 7 of the
    9 patients still on study drug.
  • Based on a current CBR of 41%, the Company estimates the 95%
    confidence interval for the CBR rate in the 9 mg cohort to be 22% to
    62% at study completion.

In addition to the CBR, the trial is evaluating the Best Overall
Response (BOR) rate of the patients, defined as a CBR at any time point
during treatment with enobosarm. Of the 22 evaluable patients:

  • 7 patients who did not show CBR at 24 weeks had stable disease earlier
    at 12 weeks, corresponding to an approximately 73% (16/22) BOR;
  • 3 patients discontinued early due to reasons other than progression,
    and therefore did not have post treatment scans; and
  • When the analysis is performed with those patients who had post
    treatment follow-up scans, the CBR is 47% (9/19), with a BOR of 84%
    (16/19).

The baseline demographics for the 22 evaluable patients are consistent
with advanced breast cancer patients who typically undergo multiple
treatments. The majority of the 22 patients in the 9 mg dose cohort were
heavily pretreated prior to study entry. On average, these patients had
4 prior hormonal therapies for the treatment of their breast cancer and
91% also received prior chemotherapy. Eight of the 22 evaluable patients
(36%) had bone-only disease, while the remaining patients had measurable
disease per RECIST.

Enobosarm 9 mg appears to be safe and generally well tolerated. The
majority of adverse events are grade 1 and 2. The most common adverse
events (occurring in ≥10% of patients) reported include nausea (31%),
fatigue (18%), and arthralgias (13%). Elevations in transaminases (ALT
and AST) during enobosarm treatment were mild with the majority being
grade 1 or 2. The independent Safety Monitoring Committee met on
December 1, 2016, and recommended that the clinical trial continue as
planned.

The trial will continue as planned with a daily dose of either enobosarm
9 mg or 18 mg until 44 evaluable patients in each cohort have been
enrolled to better characterize the CBR, evaluate secondary endpoints
and describe the safety profile of the dose levels. The Company plans to
report top-line clinical results following completion of the clinical
trial, which is anticipated to occur in mid-2017.

“From my perspective as a clinician, the results with enobosarm in
treating advanced breast cancer are encouraging. The goal for treating
advanced breast cancer patients who have exhausted other hormonal
therapies for metastatic disease and whose only treatment alternative is
chemotherapy, is to achieve stabilization of their disease,” said Dr.
Beth Overmoyer, from the Dana Farber Cancer Institute and the Harvard
Medical School, who is the lead investigator for the clinical trial.
“Stabilization of disease and delaying subsequent chemotherapy treatment
while maintaining quality of life benefits a large population of
patients with hormone-receptor positive metastatic breast cancer.”

“We are pleased that the study has demonstrated an acceptable clinical
benefit rate sooner than initially anticipated in the 9 mg cohort, which
we believe warrants further development of the drug candidate for the
treatment of advanced metastatic breast cancer,” said Robert J. Wills,
Ph.D., Executive Chairman of GTx.

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 CBR at week 24, then the trial will
proceed to the second stage of enrollment for that cohort to assess CBR
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 CBR among the first 18 evaluable
patients in each such cohort to advance to the second and final stage of
the clinical trial.

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. 17 of
the 22 patients were confirmed to be AR+, and 6 of those 17 patients
demonstrated CBR at six months. In total, 7 patients (one patient with
indeterminate AR status) achieved CBR 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 CBR as best response .
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