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WASHINGTON -- The FDA has expanded the indication of abiraterone acetate (Zytiga) to include treatment of late-stage metastatic castration-resistant prostate cancer prior to chemotherapy.

The updated approval was announced the same day that results from a safety and efficacy trial were published in the New England Journal of Medicine.

Abiraterone decreases a protein involved in testosterone production, P450 17A1, that helps curb cancer cell growth.

The drug was initially approved in 2011 for the treatment of late-stage prostate cancer in patients whose cancer had progressed after treatment with docetaxel.

Approval for the new indication was carried out as part of the agency's priority review program, the FDA said in a statement.

The phase III trial included 1,088 men with late-stage, castration-resistant prostate cancer who had not received previous chemotherapy. Patients were treated with prednisone and abiraterone or prednisone and placebo. The trial endpoints were overall survival (OS) and radiographic progression-free survival.

The median radiographic progression-free survival was 16.5 months with the abiraterone-prednisone combination and 8.3 months with prednisone-placebo (hazard ratio for abiraterone-prednisone versus prednisone-placebo 0.53, 95% CI 0.45 to 0.62, P<0.001), wrote Charles Ryan, MD, of the University of California San Francisco, and colleagues.

Over a median follow-up of 22.2 months, OS was improved with abiraterone-prednisone although the median was not reached with the combination. The median OS was 27.2 months for prednisone-placebo (HR 0.75, 95% CI 0.61 to 0.93, P=0.01).

"Abiraterone improved radiographic progression-free survival, showed a trend toward improved overall survival, and significantly delayed clinical decline and initiation of chemotherapy in patients with metastatic castration-resistant prostate cancer," the authors wrote.

Grade 3 or 4 adverse events were more common with abiraterone-prednisone and included fatigue, joint swelling or discomfort, fluid retention-related swelling, hot flush, diarrhea, vomiting, cough, high blood pressure, shortness of breath, urinary tract infection, and bruising.

Common laboratory abnormalities included low red blood cell count; high levels of alkaline phosphatase; high levels of fatty acid, sugar, and liver enzymes in the blood; and low levels of lymphocytes, phosphorous, and potassium in the blood.

The drug is marketed by Janssen Biotech of Horsham, Pa.