Multi-institutional randomized phase II trial of the epothilone B analog ixabepilone (BMS-247550) with or without estramustine phosphate in patients with progressive castrate metastatic prostate cancer

Purpose: To evaluate the antitumor activity and safety of the epothilone B analog, ixabepilone, with or without estramustine phosphate (EMP), in chemotherapy-naive patients with progressive castrate metastatic prostate cancer. Patients and Methods: Patients were randomly assigned to receive ixabepilone (35 mg/m²) by intravenous infusion every 3 weeks with or without EMP 280 mg orally three times daily on days 1 to 5. Results: Between December 2001 and October 2003, 92 patients were enrolled and randomly assigned to treatment with ixabepilone alone (45 patients) or in combination with EMP (47 patients). Grades 3 and 4 toxicities experienced by more than 5% of patients included neutropenia (22%), fatigue (9%), and neuropathy (13%) on the ixabepilone arm, and neutropenia (29%), febrile neutropenia (9%), fatigue (9%), neuropathy (7%), and thrombosis (6%) on the ixabepilone + EMP arm. Post-treatment declines in prostate-specific antigen of ≥ 50% were achieved in 21 of 44 patients (48%; 95% CI, 33% to 64%) on the ixabepilone arm, and 31 of 45 patients (69%; 95% CI, 55% to 82%) on the ixabepilone + EMP arm. In patients with measurable disease, partial responses were observed in eight of 25 patients (32%; 95% CI, 14% to 50%) on the ixabepilone arm, and 11 of 23 (48%; 95% CI, 27% to 68%) on the ixabepilone + EMP arm. Time to prostate-specific antigen progression was 4.4 months (95% CI, 3.1 to 6.9 months) on the ixabepilone-alone arm and 5.2 months (95% CI, 4.5 to 6.8 months) on the combination arm. Conclusion: Ixabepilone, with or without estramustine phosphate, is well tolerated and has antitumor activity in patients with castrate metastatic prostate cancer.