6 October 2015 - - US-based biopharmaceutical company GTx, Inc. (NASDAQ: GTXI) has enrolled the first patient into its Phase 2 clinical trial of enobosarm (GTx-024) to treat women with advanced, androgen receptor positive, triple negative breast cancer, the company said on Tuesday. Enobosarm is the company's lead product candidate and is also being evaluated in a separate Phase 2 clinical trial to treat estrogen receptor positive, AR+ breast cancer, which the company recently announced had also enrolled its first patient. The open-label, multi-centre, multinational Phase 2 clinical trial (NCT02368691) will evaluate the efficacy and safety of orally administered enobosarm in up to 55 women with advanced, AR+ TNBC. Patients will receive 18 mg of enobosarm once daily for up to 12 months. The initial stage will be assessed among the first 21 evaluable patients. If at least 2 of 21 patients achieve clinical benefit at week 16, then the trial will proceed to the second stage of enrollment of up to a total of 41 evaluable patients. Clinical benefit is defined as a complete response, partial response, or stable disease, as measured by Response Evaluation Criteria in Solid Tumors (RECIST) at 16 weeks. The trial, which is being conducted under a leadership of Dr. Hope Rugo from the University of California at San Francisco, will include investigators from more than 40 clinical trial sites in the US and abroad. Enobosarm, a selective androgen receptor modulator, has been evaluated in multiple completed or ongoing clinical trials enrolling over 1,500 subjects 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, the company said. Most recently, 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+. Six of these 17 patients demonstrated clinical benefit at six months. Seven patients in total (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% of all patients achieved clinical benefit as best response and also had increased serum PSA levels which may 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. GTx is focused on 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.