Enzalutamide in patients with non-metastatic castration-resistant prostate cancer after combined androgen blockade for recurrence following radical treatment in Japan (Japanese research for patients with non-metastatic castration-resistant prostate cancer-enzalutamide: JCASTRE-zero)—a prospective single-arm interventional study

Background The effect of enzalutamide in patients with non-metastatic castration-resistant prostate cancer after combined androgen blockade, which represents a patient profile similar to real-world clinical practice in Japan, remains unknown. Therefore, we investigate the efficacy and safety of enzalutamide after combined androgen blockade for recurrence following radical treatment in Japanese patients with non-metastatic castration-resistant prostate cancer. Methods We analyzed 66 patients with non-metastatic castration-resistant prostate cancer after combined androgen blockade for recurrence following radical prostatectomy or radiation therapy who were prospectively enrolled from October 2015 to March 2018. They received enzalutamide 160 mg orally once daily until the protocol treatment discontinuation criteria were met. The primary endpoint was prostate-specific antigen-progression-free survival, defined as the time from enrollment to prostate-specific antigen-based progression or death from any cause. The secondary endpoints included overall survival, progression-free survival, metastasis-free survival, time to prostate-specific antigen progression, prostate-specific antigen response rate, chemotherapy-free survival, and safety assessment. Results The median observation period was 27.3 months. The median prostate-specific antigen-progression-free survival was 35.0 months (95% confidence interval, 17.5 to not reached). The median overall survival, median progression-free survival, median metastasis-free survival, and chemotherapy-free survival were not reached, with the corresponding 2-year rates being 91.6%, 67.1%, 72.4%, and 85.8%, respectively. The 50% prostate-specific antigen response rate was 88.9%, with the median time being 2.8 months. In total, 42.2% of the patients experienced adverse events, with malaise being the most common. Conclusions Enzalutamide effectively manages non-metastatic castration-resistant prostate cancer after combined androgen blockade for recurrence following radical treatment. Trial registration : UMIN000018964, CRB6180007.