Can Pfizer's new breast cancer drug Talzenna really make a dent in the PARP field?

The old adage "better late than never" may seem tired, but it could be apropos for Pfizer’s newly FDA-approved PARP inhibitor, Talzenna. Pfizer picked up the drug in its $14 billion acquisition of Medivation in 2017, when it was already way behind PARP players AstraZeneca, Tesaro and Clovis Oncology—and analysts doubted the company could make a significant dent in the market.

Now, Pfizer has its chance to prove them wrong. And key to the company’s success will be expanding Talzenna’s market beyond its solo therapy in breast cancer, analysts say.

Yesterday, the FDA approved Talzenna—also known as talazoparib—to treat BRCA-mutated, HER2-negative breast cancer that's locally advanced or metastatic. The approval, which followed an FDA priority review, was based on a trial with 431 patients previously treated with chemotherapy. Trial participants who received Talzenna saw a 46% reduction in their risk of disease progression compared with those treated only with chemo. The progression-free survival benefit proved out even in patients with triple-negative breast cancer, the toughest form of the disease to treat.

The FDA approved Talzenna along with the BRACAnalysis CDx test from Myriad Genetic Laboratories, which oncologists can use to identify patients most likely to respond. Myriad Chief Medical Officer Johnathan Lancaster, M.D., Ph.D., congratulated Pfizer in a statement and estimated that about 60,000 patients diagnosed each year would benefit from genetic testing to determine their eligibility for Talzenna.

Maybe so, but those patients have other treatment options, which will complicate Pfizer's marketing task. AstraZeneca and Merck & Co. have been in the breast cancer market since January with their PARP inhibitor Lynparza, which won approval to treat BRCA-mutated disease based on clinical trial data similarly impressive to those Pfizer would later achieve.

Evercore ISI analyst Steve Breazzano told investors in a note earlier this year that he was worried about how Talzenna would fit into the breast cancer market, given that its side effect profile is slightly worse than that of Lynparza. In particular, hair loss has been reported among patients taking Pfizer’s drug, a side effect "unique among PARP inhibitors," he said.

And more competition could be on the way. Clovis Oncology is testing its PARP inhibitor, Rubraca, in breast cancer, as is Tesaro with Zejula. China’s BeiGene is also gunning for a piece of the market.

RELATED: Clovis' Rubraca pulls ahead of rivals in prostate cancer with 'breakthrough' nod

Pfizer could get a leg up on rivals by proving Talzenna’s value in treating other cancers, though. Last December, the company struck a deal with Array Biopharma to test various combinations of Array’s MEK inhibitor along with Talzenna in non-small cell lung cancer and pancreatic cancer. Pfizer is also looking at various combos for treating ovarian cancer, and it has a phase 3 program underway in prostate cancer, which is another tumor that can be caused by BRCA mutations. Pfizer "may emerge as a dark horse player in prostate," Breazzano said.

But even there, Pfizer will have to contend with some tough competition. Earlier this month, Clovis scored a breakthrough designation for Rubraca in prostate cancer from the FDA. Clovis plans to submit data to the agency in the second half of 2019 to support a potential approval in that indication, which could add as much as $580 million to Rubraca’s sales and give Clovis a leading 40% share of the PARP market, analysts estimate. Plus, all three of Pfizer's PARP rivals boast various approvals in ovarian cancer.

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