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.

  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