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FDA Approves Label Change for Prostate Cancer Drug Zytiga (Abiraterone)

Positive phase III data added

The FDA has approved a label update for Zytiga (abiraterone acetate, Janssen) plus prednisone based on a final analysis of the phase III, randomized, double-blind, placebo-controlled COU-AA-302 study, which showed that abiraterone plus prednisone significantly prolonged median overall survival (OS) compared with placebo plus prednisone in chemotherapy-naive men with metastatic castration-resistant prostate cancer (mCRPC).

After a median follow-up period of more than 4 years (49.2 months), the study demonstrated a median OS of almost 3 years (34.7 months) in the patients randomly assigned to receive abiraterone plus prednisone compared with 30.3 months in the placebo-plus-prednisone arm (hazard ratio, 0.81; P = 0.003).

In this analysis, 65% of the men in the abiraterone-plus-prednisone arm and 78% of those in the placebo-plus-prednisone arm received subsequent therapy that may prolong OS in mCRPC. This includes 44% of men in the control arm who subsequently received abiraterone plus prednisone.

Data from the final analysis were published in the February 2015 issue of The Lancet Oncology.

The FDA based its 2011 approval of abiraterone plus prednisone for the treatment of men with mCRPC prior to chemotherapy on the results from a planned second interim analysis of the COU-AA-302 trial, which included 1,088 men with mCRPC who had not received prior chemotherapy. The subjects were randomly assigned to receive abiraterone 1,000 mg administered orally once daily plus prednisone 5 mg administered twice daily or placebo plus prednisone 5 mg administered twice daily. The study’s co-primary endpoints were radiographic progression-free survival (rPFS) and OS. Key secondary endpoints included the time to opiate use and the time to the initiation of chemotherapy.

Abiraterone blocks cytochrome P450-17–mediated androgen production –– which fuels prostate cancer growth –– at three sources: in the testes, adrenals, and the prostate tumor tissue. The treatment has been proven effective in patients with mCRPC who had progressed on androgen-deprivation therapy.

Research has shown that prostate-cancer tumor cells develop adaptive mechanisms, including the ability to produce androgen, which help to fuel their survival, suggesting that reducing androgen production is key to helping men with mCRPC manage their illness.

Source: PipelineReview; March 31, 2015.

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