Zytiga Study Unblinded Following Positive Interim Analysis

The phase III COU-AA-302 study of abiraterone acetate (Zytiga) in chemotherapy-naïve patients with metastatic castration-resistant prostate cancer (mCRPC) has been unblinded following a positive interim analysis and a unanimous vote from an independent monitoring committee.

Abiraterone acetate plus prednisone is currently approved for patients with mCRPC who have already received chemotherapy with docetaxel. The goal of the COU-AA-302 study was to determine the efficacy of the agent prior to the introduction of chemotherapy.

COU-AA-302 randomized 1088 patients with mCRPC who had not received chemotherapy to receive abiraterone acetate plus prednisone or placebo and prednisone. Primary outcome measures included overall survival and progression-free survival, which were measured every 3 months by radiographic testing.

At the planned interim analysis, the data showed a clinical benefit and superior safety profile in the abiraterone acetate arm, which led to the unblinding of the placebo group. The preliminary COU-AA-302 data will likely be presented at the ASCO annual meeting in June, and regulatory approval will subsequently be sought in the latter half of 2012.

“The COU-AA-302 study has been a key priority for us as we expand our understanding of the utility of Zytiga in metastatic prostate cancer,” said William N. Hait, MD, PhD, global head of Janssen R&D, a part of Johnson & Johnson, which manufacturers Zytiga. “We’re delighted that these data will soon be added to the growing body of literature about this important medication,” Hait added.

Abiraterone acetate is a second-generation androgen deprivation therapy that inhibits the dual enzyme complex CYP17. This enzyme is implicated in the androgen synthesis that stimulates tumor growth. Additionally, abiraterone acetate is an active inhibitor of the hepatic drug—metabolizing enzyme CYP2D6, and as a result, should not be administered with other CYP2D6 substrates.

Abiraterone acetate is 1 of 5 agents now available or under investigation for similar biologic niches within prostate cancer. The results from this trial could help alleviate concerns on how to best sequence the multiple therapies now available to treat patients with prostate cancer.

Prostate cancer is the second leading cause of cancer-related death in men in the United States and an estimated 241 740 new cases will be diagnosed in 2012, according to the American Cancer Society.