Phase II study of estramustine and vinblastine, two microtubule inhibitors, in hormone-refractory prostate cancer

Estramustine phosphate (EMP) and vinblastine are two microtubule inhibitors with distinct molecular targets and at least additive antimicrotubule effects in vitro. Their modest single-agent activities in hormone-refractory prostate cancer, nonoverlapping toxicities, and lack of cross-resistance prompted a phase II trial in hormone-refractory prostate cancer.

Thirty-six assessable patients at the Fox Chase Cancer Center and seven Fox Chase Cancer Center Network institutions were treated with oral EMP 600 mg/m2 on days 1 to 42 and vinblastine 4 mg/m2 intravenously (IV) once a week for 6 weeks. Courses were repeated every 8 weeks. Response assessment was based on a change in serum prostate-specific antigen (PSA) levels and was correlated with change in pain scores.

PSA decreased from baseline by at least 50% in 22 patients (61.1%) and by > or = 75% in eight patients (22.2%). A 50% or more decrease in PSA on three successive 2-week measurements together with an improved or stable pain score, performance status, and measurable soft tissue disease (if present) was required for a partial response (PR), which occurred in 11 patients for an overall response rate of 30.5% (95% confidence interval, 15.6% to 45.6%). In seven patients with measurable nonosseous disease, there was one PR (14%) and one minor response (MR). In 28 patients with assessable pain, major pain responses occurred in 12 (42.9%). PSA response (> or = 50% decrease times three measurements) was predictive of major pain response with a 93.7% specificity, a 50% sensitivity, and a positive predictive value of 85.7%.

We conclude that EMP and vinblastine is an active combination in hormone-refractory prostate cancer.