[Efficacy and Prognostic Factors of Estracyt ® in Patients with Castration-Resistant Prostate Cancer (CRPC) : From the Data Analysis of Estracyt ® Special Drug Use Investigation].

Abstract Estracyt○R (estramustine phosphate) is a medical drug for prostate cancer with cytotoxic activity causing disruption of microtubule organization and indirect androgen production suppressing activity by its metabolite, estradiol. Based on the data obtained from the Estracyt○R Special Drug Use Investigation which surveyed the clinical efficacy and safety of Estracyt○R in patients with prostate cancer whose relapse of prostate cancer after combined androgen blockade (CAB) therapy was confirmed, we evaluated the progression-free survival, prognostic factor, decrease in prostate specific antigen (PSA) level and safety. This surveillance was conducted at 147 institutions nationwide between October, 2010 and September, 2013 and clinical efficacy was evaluated in 239 cases and safety in 329 cases. The median duration of progression-free survival, PSA progression-free survival and PSA response were 169 days (95%CI, 142-190), 197 days (95%CI, 169-267) and 385 days, respectively. The decrease in PSA level was observed in 125 cases (52.3%). Rate of PSA decline ＞50 and ＞25% were 18.4 and 43.1, respectively, and rate of PSA best response (PSA decline ＞ 50%) was 32.6%. Multivariate analysis demonstrated that long duration of prior CAB therapy, Estracyt○R - pretreatment PSA value and bone metastasis influenced progression-free survival significantly. Adverse events were observed in 127 cases (38.6%). The major adverse events were anorexia which was observed in 35 cases (10.9%), gastrointestinal disorders observed in 32 cases (9.7%), abnormal laboratory test values observed in 31 cases (9.4%) and gynecomastia observed in 16 cases (4.9%). These results suggest the clinical efficacy and safety of Estracyt○R for chemotherapy-naive castration-resistant prostate cancer (CRPC), and Estracyt○R is regarded as one of the treatment options for patients with CRPC, especially for patients who had long duration of prior CAB therapy.