Shares of Puma Biotechnology (PBYI) are down 19% after the company reported mediocre breast cancer results from a poster set to be presented at the American Society of Clinical Oncology — ASCO –meeting being held May 29 to June 2, 2015 in Chicago. Puma’s drug known as Neratinib is in a phase 3 trial treating patients with breast cancer that are HER2 positive. There are about 25% of breast cancer cases that are HER2 positive.
The phase 3 trial recruited 2,821 patients that had taken previous treatments targeted for HER2. The results were that only some patients saw an improvement in disease-free survival and even then only by 2.3 months. The company had disclosed that Neratinib showed a 33% increase in disease-free survival in a previous study.
Patients were split up into two different dose groups. One set of patients took Neratinib, breast cancer drug Herceptin and chemotherapy; the other group of patients were treated with Herceptin and chemotherapy only. After 2 years in the trial patients taking Neratinib combo drugs saw a 93.91% survival without their disease progressing. This compares to the placebo arm whereby patients achieved a 91.6% survival without their disease progressing.
Analysts and investors were disappointed because they were expecting a 3% difference between the drug combo and placebo combo. Unfortunately their was only a 2.3% difference. To make matters worse the trial saw 40% of the patients had serious diarrhea. Therefore including the small improvement in disease free survival, along with the great risk for severe diarrhea leaves the company with a potential problem with the FDA.
