Pfizer and Astellas abandon efforts to expand Xtandi into breast cancer

Pfizer HQ
After assessing phase 2 data and the competitive landscape in breast cancer, Pfizer and Astellas have decided to stop developing their prostate cancer drug as a treatment for that form of the disease.

There is troubling news for Pfizer and cancer med Xtandi, one of the assets it picked up in its $14 billion deal last year for Medivation. The drug giant and its partner Astellas have given up their trials of Xtandi in breast cancer.

Xtandi, which is already approved for treating prostate cancer, is shared with Tokyo-based drugmaker Astellas. The drug generated more than $2.2 billion last year, but Astellas has also been investigating it as a treatment for breast cancer as well as for liver cancer. In its July pipeline update (PDF), Astellas said that had discontinued the breast cancer program.

The note, which affirms a disclosure first made in May, says the decision came after comprehensive discussions with Pfizer about a “competitive landscape change, need for further diagnostic development and new phase 2 data.”

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In an email today Astellas spokesman Tyler Marciniak confirmed that the development program had been discontinued, saying that no clinical trials had to be halted because “no patients were ever enrolled in the planned ENDEAR trial.”

After evaluating data from phase 2 trials, the companies decided not to proceed—not because of any specific data, but because of Astellas' evolving perspective, Marciniak explained.  Researchers decided there was a need to better understand the role of androgen signaling in breast cancer for the AR inhibitor to potentially work.

“Additionally, expanded analysis was needed to identify the optimal genetic signature for breast cancer patients most likely to benefit from enzalutamide,” Marciniak explained.

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The breast cancer move is another shift in expectations for Xtandi since Pfizer bought Medivation last year, when it outmaneuvered Sanofi to snatch the California-based biotech at a price that some analysts considered very rich.

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When the deal was announced a year ago, Bernstein analyst Tim Anderson estimated Medivation's take from Xtandi would be about $1.8 billion by 2021, although other analysts noted that med's growth had slowed

Xtandi is reportedly facing reimbursement challenges as well as the threat of generic versions of Janssen’s key competitor Zytiga, which would hurt Pfizer’s pricing power in the field.

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It comes at a sensitive time for the Pfizer, which later this year will lose patent protection on its legendary erectile dysfunction drug Viagra and then lose exclusivity next year on  nerve pain treatment Lyrica. The two drugs generated a combined $4.2 billion in the U.S. last year for Pfizer last year.

Analysts at Credit Suisse, which recently downgraded the Big Pharma player, has said they do not expect drugs that Pfizer got in the buyout of Medivation and is $4.5 billion for Anacor to offset sales that would be lost by Pfizer in the near term.  

Editor's note: This story was updated to emphasize that the decision to stop Xtandi development in breast cancer was jointly made between Pfizer and Astellas.