Pfizer and Astellas' stalwart prostate cancer med Xtandi has watched as Johnson & Johnson's challenger, Erleada, picked up the lead in the metastatic, castration-sensitive form of the disease. But now, Xtandi is ready to take on its familiar foe with a new green light of its own.

The FDA on Monday approved Xtandi as a treatment for metastatic, castration-sensitive prostate cancer (mCSPC), making it the only drug approved in that indication as well as in metastatic and non-metastatic, castration-resistant prostate cancer. 

The new approval will open Xtandi up for use in a patient population that includes about 40,000 U.S. males each year, Pfizer said in a release. And to get it out to them, the Pfizer-Astellas team will lean on its extensive network of oncologists. That marketing effort has translated to 420,000 patients treated since the drug was initially approved in 2012, Pfizer said.

"There is significant physician and comfort with Xtandi so we hope that this approval will build upon that," Chris Boshoff, Pfizer Oncology's chief development officer, said ahead of the approval.

The FDA based its approval on data from the phase 3 Arches trial that showed a combination of Xtandi and androgen-deprivation therapy (ADT) reduced the risk of cancer worsening or death by 61% versus ADT alone.

In a second investigator-sponsored study, dubbed Enzamet, Xtandi pared down the risk of death by 33% compared with other non-steroidal androgen-fighting drugs.

Xtandi's approval comes three months after Erleada earned an approval in mCSPC, following the FDA's real-time review of the drug’s phase 3 Titan trial. Data from that study showed Erleada plus ADT cut the risk of death over placebo plus ADT by 33%. After nearly two years, 84% of patients on Erleada-ADT were still alive, compared with 78% of the placebo-ADT group.

So, far, Xtandi has a resounding lead over Erleada in terms of worldwide sales, with Pfizer's share of the revenue at $594 million in the first nine months of the year. Newer to the market, Erleada isn't listed separately in J&J's most recent earnings report. 

If history is any indication, Erleada could have some trouble keeping up with Xtandi in its new indication. In the six months following Xtandi's FDA nod in non-metastatic, castration-resistant prostate cancer, the older drug quadrupled Erleada's share of the market—despite Erleada's four-month head start.

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