A meta-analysis of individual patient data from randomized trials assessing chemotherapy with and without estramustine in patients with castration-refractory prostate cancer

Abstract

4561 Background: Estramustine phosphate is a mustard-estradiol conjugate, with evidence of both hormonal and non-hormonal effects. In phase II trials, the response rates of microtubule inhibitors are increased when combined with estramustine. Morbidity includes notably thrombosis in about 7% of cases. Whether combining estramustine with chemotherapy increases survival in castration-refractory prostate cancer (CRPC) is still controversial. Methods: Data from all published and unpublished prospective randomized trials assessing chemotherapy + estramustine versus chemotherapy alone in CRPC were sought using electronic database searching, hand searching, and by contacting experts in the field. The primary endpoint was overall survival (OS). The analysis was performed on an intention-to-treat basis. The stratified logrank test was used and an overall hazard ratio (HR) was computed using a fixed effect model. χ2 heterogeneity tests were used to test for statistical heterogeneity. All p-values were two-sided. Multivariate analysis was performed using a Cox model stratified by trial. Results: Individual data were obtained from all 5 randomized trials conducted in the PSA era that had been identified (n = 610). The control arms consisted of docetaxel (1), paclitaxel (1), ixabepilone (1), and vinblastine (2). With a median follow-up of 2.8 years, 510 deaths had occurred. OS was significantly better in the estramustine arm (HR = 0.82 [95% CI: 0.69–0.97]; p = 0.02). Overall, the risk reduction (RR) of death related to estramustine was 18% (± 8). There was no significant interaction (p = 0.66) between the RR of trials using vinblastine (RR = 15% [± 12]) and in those using taxanes or ixabepilone (RR = 21% [± 11]). The estimated 1-year OS rate was 57% and 50% in the estramustine arm and in the control arm, respectively. The 18-months OS rate was 43% and 35%, respectively. There was no interaction between the effect of estramustine and age, performance status, or serum PSA in the Cox model. Conclusions: Combining estramustine with chemotherapy increases OS over chemotherapy alone in patients with castration-refractory prostate cancer. [Table: see text]