ASCO: Pfizer, Astellas' Xtandi racks up more data for new prostate cancer approval

CHICAGO—Pfizer and Astellas’ Xtandi is gunning for a new indication in prostate cancer, and they say Sunday's new data complement the supporting evidence they’ve already generated.

Sunday at the American Society of Clinical Oncology annual meeting, researchers trumpeted data from an investigator-sponsored study in metastatic hormone-sensitive prostate cancer (mHSPC). The study showed Xtandi slashed the risk of death by 33% compared with other non-steroidal androgen-fighting drugs.

Eighty percent of men taking the Pfizer-Astellas drug were alive after three years compared with 72% of men who received the hormone-based chemo drugs bicalutamide, nilutamide or flutamide alongside standard treatment.

The results from the phase 3 study, dubbed Enzamet and led by the Australian and New Zealand Urogenital and Prostate Cancer Trials Group, back up the companies’ own results from the phase 3 Arches trial. “The two studies actually are complementary of one another,” said Andrew Krivoshik, M.D., Astellas' vice president of medical science for oncology. The types of patients overlapped, but endpoints and eligibility criteria differed, he said.

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And both studies will help support Pfizer and Astellas' regulatory filing for a label expansion, Andy Schmeltz, global president and general manager of Pfizer Oncology, said. 

"We think the totality of the data together makes a pretty compelling platform for physicians to consider Xtandi, assuming it gets approved, in this patient population," he added.

Arches, detailed in February, showed that combining Xtandi and androgen deprivation therapy (ADT) cut the risk of cancer worsening or death by 61% versus ADT alone. At the time of analysis, patients in the ADT-only group had gone a median 19.4 months before showing evidence of radiographic disease progression, an endpoint commonly used in prostate cancer trials. Meanwhile, in the Xtandi-ADT group, the median hadn’t yet been reached.

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At the time, Pfizer and Astellas said they’d take the results to regulators worldwide, aiming to tack an HSPC nod onto Xtandi’s list of approved uses. Right now, the product is cleared only in castration-resistant prostate cancer.

And given Xtandi's prostate market battle with Johnson & Johnson treatments Zytiga and Erleada, the partners wouldn’t mind a sales boost; the drug's $168 million in first-quarter sales missed Wall Street’s $186 million prediction. Pfizer biopharma President Angela Hwang cited inventory differences and Pfizer’s free drug program among reasons Xtandi’s revenues have been lagging behind demand.