Low-Dose Estramustine Phosphate and Concomitant Low-Dose Acetylsalicylic Acid in Heavily Pretreated Patients With Advanced Castration-Resistant Prostate Cancer

Background: The aim of this phase 2 study was to evaluate the activity and tolerability of low-dose estramustine phosphate (EMP) with concomitant low-dose acetylsalicylic acid (ASA) as a thromboprophylactic agent in heavily pretreated patients with advanced castration-resistant prostate cancer. Methods: Patients received 420 mg of oral EMP twice daily and oral ASA 100 mg once daily. The primary endpoint was prostate-specific antigen response. All of the patients had been previously treated with docetaxel and abiraterone acetate, and 12 had also received cabazitaxel. Results: Thirty-one patients were enrolled. Prostate-specific antigen response was observed in 9 patients (29.0%; 95% confidence interval [CI], 14-48). Median progression-free survival was 3.6 months (95% CI, 2.2-5.6), and median overall survival was 7.6 months (95% CI, 6.9-9.7). Treatment was generally well tolerated, and no grade 3/4 toxicity was observed. Ten patients (32.2%) had grade 2 nausea and vomiting. No cardiovascular event and no major bleeding occurred. No venous thromboembolism event was observed. Conclusion: Low-dose EMP with concomitant low-dose ASA seems to be a safe treatment option with some activity for patients with advanced castration-resistant prostate cancer who have been heavily pretreated.