PARP battle heats up as Pfizer nabs priority review for talazoparib in breast cancer

Pfizer building
Pfizer's PARP inhibitor, talazoparib, produced a progression-free survival benefit in several subsets of breast cancer patients. (Tracy Staton)

Last year at this time, Pfizer’s $14 billion purchase of Medivation was being cited as a cautionary tale of M&A gone wrong, after one product of that deal—prostate cancer drug Xtandi—turned in disappointing data at the annual confab of the American Society of Clinical Oncology (ASCO). Pfizer also paid top dollar for Medivation for its experimental PARP inhibitor, talazoparib, but that drug was facing stiff competition from AstraZeneca, Tesaro, Clovis Oncology and others.

Now things are finally looking up for Pfizer. The company announced that the FDA has granted priority review for talazoparib in patients with BRCA-mutated, HER2-negative breast cancer. Pfizer is expecting a decision by December, and the European Medicines Agency is also reviewing its application for approval in the same patient population.

RELATED: Pfizer's $14B Medivation deal's now a cautionary M&A tale, thanks to ASCO: analyst

Still, Pfizer will be very late to the PARP party. In January, AstraZeneca and its partner Merck won FDA approval for their first-in-class drug Lynparza to treat patients with BRCA-mutated breast cancer. That approval came after AZ posted data at last year’s ASCO showing that Lynparza cut the risk of disease progression or death by 42%. It also produced tumor shrinkage in 60% of patients, while only 29% of patients in the chemo arm of the study saw their tumors diminish.

And there could be even more competition in the future. Clovis Oncology’s Rubraca and Tesaro’s Zejula are both being tested in breast cancer, including in combination trials with immune-boosting checkpoint inhibitors from Merck and Bristol-Myers Squibb. AstraZeneca is also testing Lynparza in combination with Merck’s checkpoint inhibitor Keytruda—an arrangement that was part of their $8.5-billion tie-up last July.

RELATED: AstraZeneca's Lynparza, now in hot PARP battle, posts 42% survival win in breast cancer

The FDA granted priority review to talazoparib in breast cancer based on results from the pivotal trial Embraca, according to Pfizer. In December, the company announced that that patients taking the PARP inhibitor had a 46% reduction in the risk of disease progression over patients treated with chemotherapy. During the trial, the progression-free survival benefit was seen across several subgroups of patients, including those with hard-to-treat triple-negative breast cancer, the company said.

BRCA mutations are implicated in more than 25% of inherited breast cancers and between 5% and 10% of all incidences of the disease, according to data cited by Pfizer. Patients with BRCA mutations are generally diagnosed in their 40s, making them two decades younger than the broader breast cancer patient population. When AstraZeneca’s PARP inhibitor was approved to treat breast cancer, one of the company’s executives predicted BRCA testing upon diagnosis of the disease would become routine.

That could boost Pfizer’s sales of talazoparib, to be sure, but it may not mute critics who still wonder if Medivation was worth $14 billion. In the summer of 2016, before Pfizer made its takeover bid, Medivation CEO David Hung told his company’s investors that any acquirer would need to place a premium on talazoparib, which he called “best in class.” But as Pfizer prepares to enter an increasingly competitive market, the question of whether that acquisition will live up to the high expectations set by its price tag remains to be answered.