Synta Pharmaceuticals announced presentation of results from the ENCHANT-1 trial, a single-arm multi-center Phase 2 proof-of-concept study designed to evaluate ganetespib, the company’s lead drug candidate, administered as monotherapy for the treatment of metastatic breast cancer. The results are being presented during a poster session at the 2013 San Antonio Breast Cancer Symposium in San Antonio, Texas. The ENCHANT-1 trial is designed to evaluate the efficacy and safety of ganetespib monotherapy for treatment of HER2+ or triple-negative breast cancer patients previously untreated for locally advanced or metastatic disease. A third cohort was recently added to evaluate ganetespib in ER/PR+, HER2- patients. The goal of the window-of-opportunity trial design is to obtain initial evidence of the presence or absence of clinical activity for single-agent ganetespib in patients diagnosed with advanced breast cancer during a 12-week period prior to first-line treatment. Per protocol, all patients enrolled are to receive baseline PET and CT scans, a PET scan at week 3 to assess metabolic response, and subsequent CT scans every 6 weeks to measure best objective response via modified RECIST 1.1 criteria. Continuation of treatment with ganetespib, or the combination of ganetespib and standard-of-care, after the 12-week initial assessment period is at investigator discretion. Target enrollment is 35 patients in each cohort, with an interim analysis planned at N=15. At the time of interim analysis conducted earlier this year, five patients were enrolled into the HER2+ cohort and 15 patients were enrolled into the TNBC cohort. Of these, four patients in the HER2+ cohort and 11 patients in the triple-negative cohort were evaluable by independent review for objective response, per proctocol. Of the four patients in the HER2+ cohort evaluable for objective RECIST response by independent review, three patients (75%) achieved an objective response, including one complete radiological response and two partial responses. One patient (25%) in this cohort achieved stable disease. At the week 3 PET assessment for metabolic response, three of the four patients (75%) evaluable by independent review in the HER2+ cohort achieved a metabolic response. In the triple-negative cohort, four of the 11 patients (36%) evaluable by independent review achieved a week 3 metabolic response. Consistent with previously reported results, diarrhea, fatigue, and nausea were the most common adverse events associated with ganetespib treatment, and were mostly Grade 1 or 2 in severity.