WALTHAM, Mass., July 23, 2013 (GLOBE NEWSWIRE) -- TESARO, Inc. (Nasdaq:TSRO), an oncology-focused biopharmaceutical company, today announced that it has initiated patient enrollment in a Phase 3 trial of niraparib, an inhibitor of poly ADP-ribose polymerase (PARP), for the treatment of ovarian cancer. This trial, referred to as NOVA, will evaluate a single daily 300 milligram dose of niraparib in 360 patients with high grade serous, platinum sensitive, relapsed ovarian cancer compared to placebo. "We are pleased to open this Phase 3 trial of niraparib to patients with ovarian cancer," said Mary Lynne Hedley, Ph.D., President of TESARO. "This milestone represents a significant advance in the progression of TESARO's pipeline and brings us closer to our goal of delivering new oncology therapies to patients." Final results from a Phase 1 trial of niraparib were presented on June 4 at the American Society of Clinical Oncology (ASCO) annual meeting in Chicago. These data showed that at the recommended dose, 75% (three of four patients) with platinum sensitive high grade serous ovarian cancer (HGSOC) achieved a RECIST response. Across all dose levels (30 milligrams to 400 milligrams daily), a RECIST response rate of 46% (6/13 patients) was observed in this population. A RECIST response rate of 50% (5/10 patients) was achieved in patients with platinum sensitive ovarian cancer and germline BRCA mutations. The median duration of response was 431 days for platinum sensitive germline BRCA patients and 444 days for platinum sensitive patients who were not germline BRCA mutation carriers. The patients with ovarian cancer who were enrolled in this study had received a median of six previous regimens of systemic therapy. Niraparib was generally well tolerated at 300 milligrams daily, with a low rate of grade 3/4 toxicities. The most frequently observed adverse events at the 300 milligram dose included grade 1/2 anemia, fatigue and nausea.