Activity of abiraterone acetate (AA) in metastatic castration-resistant prostate cancer (mCRPC) patients (pts) previously treated with ketoconazole (keto): A prospective phase II study from the Prostate Cancer Clinical Trials Consortium.

5039 Background: AA, like keto, inhibits CYP17, the rate-limiting enzyme in androgen synthesis. Since pts with prior keto were excluded from the pivotal phase III AA trials, the utility of AA following keto is not well understood. This prospective study evaluated the efficacy of AA in pts previously treated with keto. Methods: Pts with progressive mCRPC, prior keto ≥28 days, and normal baseline organ function were treated with AA 1000mg PO daily and prednisone 5mg PO BID. Pts with prior chemotherapy were excluded. Serum androgen levels, including dehydroepiandrosterone (DHEA), were measured by liquid chromatography/mass spectrometry (LC/MS) at baseline and during treatment for exploratory analyses. Radiographic progression-free survival (rPFS) was defined as freedom from death, radiographic progression, or unequivocal clinical progression. Results: 42 pts were enrolled. Median duration of prior keto was 38 weeks (wks). 40 pts discontinued keto due to disease progression, and 2 due to toxicities. AA result...