FDA Approves Earlier Use of Abiraterone Acetate

Charles J. Ryan, MD

The FDA has approved abiraterone acetate (Zytiga) in combination with prednisone prior to chemotherapy for the treatment of men with metastatic castration-resistant prostate cancer (mCRPC).

The FDA initially approved abiraterone acetate in 2011 following docetaxel for men with mCRPC. The expanded indication may quadruple the number of patients eligible for treatment with this agent.

"This expanded indication for Zytiga helps fill a critical medical need, providing physicians an important tool for treating men with metastatic castration-resistant prostate cancer who have not received chemotherapy," said Charles J. Ryan, MD, University of California San Francisco Helen Diller Family Comprehensive Cancer Center.

The new indication was approved based on the phase III COU-AA-302 trial in which 1088 men were randomly selected to receive prednisone plus either abiraterone acetate or a placebo. The coprimary endpoints of the trial were radiographic progression-free survival (rPFS) and overall survival (OS).

In March, the study was unblinded and patients in the placebo arm were allowed to cross over to receive abiraterone acetate. The unanimous recommendation to unblind the study was based on findings of clinical benefit by an independent data monitoring committee.

At the unblinding, 43% of total events had been reported. The rPFS had not been reached in the abiraterone acetate arm compared to 8.28 months in the control (hazard ratio [HR] = 0.425; 95% CI, 0.347, 0.522; P < .0001). Additionally, OS had not been reached in the investigational arm and was 27.2 months in the control (HR = 0.75; 95% CI, 0.61, 0.93; P = 0.0097).

According to The New England Journal of Medicine, at a second interim analysis, the median rPFS was 16.5 months with abiraterone acetate compared to 8.3 months in the control arm (HR = 0.53; 95% CI, 0.45, 0.62; P < .001). Additionally, the median time to initiate chemotherapy was 25.2 months in the abiraterone acetate arm compared with 16.8 months for placebo (HR = 0.580; 95% CI, 0.487, 0.691; P < .0001).

In its approval notice, the FDA cited the median OS for those in the abiraterone acetate arm as 35.3 months compared with 30.1 months for those receiving placebo (hazard ratio [HR] = 0.792; 95% CI, 0.655, 0.956; P = .0151). According to prespecified values, the median OS was not deemed statistically significant.

The most common grade 3 and 4 adverse events were hypertension, hypokalemia, elevated ALT levels, and elevated AST levels. The most common all grade adverse reactions were fatigue, joint swelling, edema, hot flush, diarrhea, and vomiting.

“Today’s approval demonstrates the benefit of further evaluating a drug in an earlier disease setting and provides patients and healthcare providers the option of using Zytiga earlier in the course of treatment,” said Richard Pazdur, MD, director of the Office of Oncology Drug Products in the FDA’s Center for Drug Evaluation and Research, in a press release.

According to the National Cancer Institute, 241,740 men will be diagnosed with prostate cancer in 2012.