Puma Cancer Drug Suffers "Approvability Risk" On Extreme Side Effect

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Neratinib is suffering greater "approvability risk" after Puma Biotechnology (PBYI) said Wednesday it had to add a second anti-diarrheal to the breast cancer regimen, prodding shares to a three-week low Thursday.

RBC analyst Simos Simeonidissees regulators questioning neratinib"s toxicity profile. Neratinib is used to treatHER2-positive early- and late-stage breast cancer. Diarrhea is a common side effect. In a prior phase 3 trial, 95.4% of patients experienced some form of diarrhea.

On Wednesday, Puma unveiled the results of a phase 2 trial aiming to cut down on neratinib-related diarrheaby combining with anti-diarrheal drugsloperamide and budesonide. Of the 40 patients on the combo, 15% experienced grade 3 diarrhea or above.

That compares with 25%-29% of 135 loperamide-alone patients who suffered grade 3 or above diarrhea.The median number of episodes was one with a median of three days" duration. In combination patients, the median number of days was 2.5 for one episode.

Simeonidisnotes the loperamide-alone data was much worse vs. Puma"s year-earlier presentation at the San Antonio Breast Cancer Symposium. Then, 16% of patients suffered neratinib-related diarrhea while also taking loperamide.

"A comparison of the graphs from last year"s SABCS distribution of grade 1-4 diarrhea shows that grade 3 only occurred in the first month," he wrote in a report. "However, this year"s presentation shows that grade 3 events occur during the first four months of treatment."

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Still, Simeonidis believes neratinib should garner U.S. Food and Drug Administration and European Medicines Agency approvals. Though he wonders whether regulators might hesitate on the drug"s toxicity.

"The recent second negative regulatory surprise for investors increases the approvability risk for neratinib in the form of, "What else could come up that we assumed we were OKwith?"" he wrote.

Credit Suisse analyst Kennen MacKay was more bullish on neratinib and called the results "encouraging." No patient discontinued neratinib use in the most recent trial as a result of diarrhea.

Neratinib alone increased progression-free survival (PFS) by three months with an objective response rate (ORR) of 33%. In combination with chemotherapyfulvestrant, PFS increased by 3.7 months and ORR hit 58%.

Simeonidiskept his sector perform rating on puma stock. mackay has an outperform rating and 111 price target on Puma stock. In early trading on the stock market today, Puma stock slipped as much as 9.4%, touching a three-week low. Midday, it was down 8%, near 36.50.

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Source: http://www.investors.com/news/technology/puma-cancer-drug-suffers-approvability-risk-on-extreme-side-effect/