FDA Expands Label for Abiraterone Acetate (Zytiga) in Metastatic Prostate Cancer

The US Food and Drug Administration (FDA) has expanded the approved use of abiraterone acetate (Zytiga) to treat men with metastatic castration-resistant prostate cancer prior to receiving chemotherapy. The drug was initially approved in April 2011 for use in patients whose prostate cancer progressed after treatment with docetaxel.

“Today’s approval demonstrates the benefit of further evaluating a drug in an earlier disease setting and provides patients and health care 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.

The trial that led to the expanded approval was a clinical study of 1,088 men with late-stage, castration-resistant prostate cancer who had not been treated with chemotherapy. Participants received prednisone in combination with either abiraterone acetate or placebo. The study was designed to measure overall survival radiographic progression-free survival.

Patients who received the prednisone/abiraterone acetate combination had a median overall survival of 35.3 months compared with 30.1 months for those receiving prednisone/placebo.

Results from the study also showed an improvement in radiographic progression-free survival for those patients receiving abiraterone acetate. The median radiographic progression-free survival was 8.3 months in the placebo group and had not yet been reached at the time of analysis for patients treated with abiraterone acetate (hazard ratio, 0.43; 95% confidence interval, 0.35–0.52; P < .001).

Grade 3 or 4 adverse events in the prednisone/abiraterone acetate arm of the trial were reported in 48% of patients compared to 42% of patients in the prednisone/placebo arm. Serious adverse events were reported in 33% and 26% of patients, and adverse events that resulted in death were reported in 4% and 2% of patients, respectively.

The most common adverse events associated with abiraterone acetate include fatigue, peripheral edema, arthralgia, diarrhea, vomiting, high blood pressure, shortness of breath, cough, urinary tract infection, and bruising.

Grade 3 or 4 hepatotoxicity-related adverse events consisted primarily of a reversible elevation in aminotransferase levels (8% of patients in the prednisone/abiraterone acetate arm vs 3% of patients in the prednisone/placebo group).