Estramustine Phosphate Monotherapy in Castration-Resistant Prostate Cancer Patients Who Cannot Receive Cytotoxic Chemotherapy

ABSTRACT

Purpose@#To investigate whether estramustine phosphate (EMP) monotherapy is applicable to castration-resistantprostate cancer (CRPC) patients who cannot receive cytotoxic chemotherapy. @*Materials and Methods@#This retrospective single-arm study was conducted in CRPC patients who had notexperienced cytotoxic chemotherapy and received EMP monotherapy (560 mg/day) at 2 institutions from 2008to 2017. We analyzed prostate-specific antigen (PSA) responses, overall survival, and adverse effects of EMPtreatment. @*Results@#A total of 28 patients were analyzed. A reduction in serum PSA was observed in 11 patients (39.3%).Seven cases (25.9%) achieved more than 25% reduction of PSA, and 5 of them (18.5%) experienced more than50% reduction. Median overall survival was 23 months (interquartile range, 10–60 months). Multivariable analysesdemonstrated that low level of PSA at diagnosis of CRPC and long duration of prior androgen deprivation therapywere independent favorable factors predicting long-term overall survival. Adverse effects were edema (n=2; grade2), nausea/vomiting (n=1; grade 2), gynecomastia (n=1; grade 2), and dyspnea (n=1; grade 1). Neither thromboembolicevent nor grade 3–5 toxicity was observed. There was no discontinuation caused by side effects ofEMP. @*Conclusions@#EMP monotherapy could be considered as a safe treatment option with some effectiveness for CRPCpatients who did not undergo cytotoxic chemotherapy. EMP is not generally recommended anticancer drug in thecurrent guidelines for CRPC, but EMP monotherapy is thought to have an alternative role when a standard treatmentcannot be selected due to patient's age, health condition, or comorbidity.