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.