Puma Biotechnology, Inc. (PBYI) Down on Disappointing Drug Trials
Shares of Los Angeles, CA, based Puma Biotechnology, Inc. (PBYI) fell sharply on Tuesday, on a day that was mildly lower in stocks overall. Puma dropped $23.32 per share, down 13.72%, to close at 146.65 on volume of 3,602,943 shares. The stock continued to sell off following Monday's announcement by a cancer expert that the company's promising anti-cancer drug, neratinib, produces only very small improvements in breast cancer patients.
Puma's stock declined 9% on Monday, in reaction to comments by Dr. Harold Burstein, a breast cancer expert from the Dana-Farber Cancer Institute. Burstein reported that patients treated with Puma's drug, neratinib - in development for the treatment of HER2-positive breast cancer - showed only a very small improvement in their condition, compared with those in the placebo group. In addition, the drug produced grade 3 diarrhea in 40% of the patients who are on the drug therapy. Grade 3 diarrhea involves at least seven stools per day, incontinence, and even hospitalization.
The trials involved 2,840 patients who were treated with either neratinib, or with a placebo, for one year. Following the treatment, patients continued to be monitored for a recurrence of the disease for an additional year.
The report was the result of the neratinib Phase III "ExteNET study at the American Society of Clinical Oncology (ASCO). Test results showed that the absolute disease-free survival for patients treated with neratinib was 93.9%, compared to 91.6% for those in the group treated with a placebo. The difference between the two outcomes is just 2.3%. It is not clear if the benefit of the drug therapy outweighs the high incidence of grade 3 diarrhea.
In addition, the relatively short follow-up period of just two years is considered insufficient to prove the benefit of the drug with any degree of certainty. This could lead to the possibility that the FDA may ask for more data, further delaying the introduction of the drug to the market.
Puma executives see the outcome differently.
"We are very pleased with the results of the ExteNET trial with neratinib. This represents the first trial with a HER2 targeted agent that has shown a statistically significant benefit in the extended adjuvant setting, which we believe provides a meaningful point of differentiation for neratinib in the treatment of HER2 positive breast cancer... said Alan H. Auerbach, Chief Executive Officer and President of Puma. "We look forward to proceeding with the regulatory filing for neratinib for the extended adjuvant treatment of breast cancer currently anticipated in the first quarter of 2016.
Since neratinib is not expected to be available until next year, the company has another year to collect data on the patients that were part of the ExteNET study. The company also noted that the trials indicated that the incidence of grade 3 diarrhea could be substantially reduced in patients who are receiving preventative treatments.
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