SEATTLE, WA, Oct. 7, 2013 /PRNewswire/ - Oncothyreon Inc. (NASDAQ: ONTY) today announced the presentation of final results from the first Phase 1 trial of ONT-380 at the American Association for Cancer Research Special Conference on Advances in Breast Cancer Research in San Diego. The results were presented by Virginia F. Borges, M.D., Associate Professor in the Division of Medical Oncology, University of Colorado School of Medicine. ONT-380 (also known as ARRY-380) is an orally active, reversible and selective small-molecule HER2 inhibitor being developed by Oncothyreon in collaboration with Array BioPharma Inc. (Nasdaq: ARRY), Boulder, Colorado. The first-in-human Phase 1 trial, with both dose-escalation and expansion components, enrolled a total of 50 patients, 43 of whom had HER2+ metastatic breast cancer. In this study, ONT-380 demonstrated an acceptable safety profile; treatment-related adverse events were primarily Grade 1. Because ONT-380 is selective for HER2 and does not inhibit EGFR, there was a low incidence and severity of treatment-related diarrhea, rash and fatigue, side effects which have been associated with EGFR inhibition. A single patient experienced Grade 2 treatment-related diarrhea and no patient developed treatment-related Grade 3 diarrhea; one patient had a Grade 3 rash. Additionally, there were no treatment-related cardiac events or Grade 4 treatment-related adverse events reported. The maximum tolerated dose of ONT-380 established in this Phase 1 trial was 600 mg twice daily. The dose-limiting toxicity was reversible elevation in liver enzymes. In this trial, 22 HER2+ breast cancer patients with measurable disease were treated with ONT-380 at doses greater than or equal to 600 mg BID. In this heavily pretreated patient population, there was a clinical benefit rate (partial response [n = 3] plus stable disease for at least 6 months [n = 3]) of 27%. Notably, two of the patients with partial responses during treatment with ONT-380 had confirmed progressions while on prior lapatinib- and trastuzumab-containing regimens.