BACKGROUND: AT-101 (A), a small molecule oral inhibitor of the Bcl-2 family, has activity alone and in combination with docetaxel (Taxotere) and prednisone (DP) in metastatic castration-resistant prostate cancer (mCRPC). A randomized, double-blind, placebo-controlled phase II trial compared DP combined with either AT-101 (A) or placebo in chemonaive mCRPC. PATIENTS AND METHODS: Men with progressive mCRPC despite androgen deprivation were eligible and randomized 1:1. Patients received docetaxel (75 mg/m2 day 1) and prednisone 5 mg orally twice daily every 21 days with either AT-101 (40 mg) or placebo twice daily orally on days 1-3. The primary end point was overall survival (OS). RESULTS: Two hundred and twenty-one patients were randomly assigned. Median OS for AT-101 plus docetaxel-prednisone (ADP) and placebo-DP was 18.1 versus 17.8 months [hazard ratio (HR) 1.07, 95% confidence interval 0.72-1.55, P=0.63]. Secondary end points were also not statistically different. Grade 3/4 toxic effects for ADP versus placebo-DP were cardiac events (5% versus 2%), lymphopenia (23% versus 16%), neutropenia (47% versus 40%), ileus (2% versus 0%) and pulmonary embolism (6% versus 2%). In a subgroup of high-risk mCRPC (n=34), outcomes appeared to favor ADP (median OS 19 versus 14 months). CONCLUSIONS: AT-101 was tolerable but did not extend OS when combined with DP in mCRPC; a potential benefit was observed in high-risk patients.