Outcome of loco-regional radiotherapy in metastatic castration-resistant prostate cancer patients treated with abiraterone acetate

Purpose To evaluate the potential benefit of curative radiotherapy (RT) to the primary tumor in metastatic castration-resistant prostate cancer (mCRPC) patients treated with abiraterone. Materials and methods The clinical parameters of 106 mCRPC patients treated with abiraterone were retrospectively evaluated. Patients were either oligometastatic (<= 5 metastases) at diagnosis or became oligometastatic after the systemic treatment was analyzed. Local RT to the primary tumor and pelvic lymphatics was delivered in 44 patients (41%), and 62 patients (59%) did not have RT to the primary tumor. After propensity match analysis, a total of 92 patients were analyzed. Resultsn Median follow-up time was 14.2 months (range: 2.3-54.9 months). Median overall survival (OS) was higher in patients treated with local RT to the primary tumor than in those treated without local RT with borderline significance (24.1 vs. 21.4 months; p=0.08). Local RT to the prostate and pelvic lymphatics significantly diminished the local recurrence rate (16 patients, 31% vs. 2 patients, 5%; p=0.003). In multivariate analysis, the prostate specific antigen (PSA) response >= 50% of the baseline obtained 3 weeks after abiraterone therapy was the only significant prognostic factor for better OS and progression-free survival (PFS). Patients treated with primary RT to the prostate had significantly less progression under abiraterone and a longer abiraterone period than those treated without local prostate RT. Conclusions Local prostate RT significantly improved OS and local control in mCRPC patients treated with abiraterone. The patients treated with primary RT had significantly less progression under abiraterone and a longer abiraterone period than those treated without local prostate RT.