Safety and feasibility of radiation therapy to the primary tumor in patients with metastatic castration-resistant prostate cancer

Abstract Objectives To evaluate safety and feasibility of radiation therapy (RT) to the primary tumor in patients with metastatic castration-resistant prostate cancer (mCRPC). Patients and Methods This retrospective study included 105 patients with mCRPC who were treated between April 2004 and May 2019. We divided the patients into two groups: patients treated with RT to the primary tumor after they developed castration-resistant prostate cancer (CRPC) (RT group) and without (non-RT group). The primary purpose was safety assessed using the Common Terminology Criteria for Adverse Events. The secondary purpose included prostate-specific antigen (PSA) response, cancer-specific survival (CSS), and overall survival (OS). Background-adjusted multivariate analyses, with the inverse probability of treatment weighting (IPTW) method were performed to evaluate impact of RT on CSS and OS. Results The median age at CRPC diagnosis was 75 years, and the median follow-up period after CRPC diagnosis was 21 months. The adverse events rates related with RT in any grade and grade ≥3 were 55% and 23%, respectively. Nine patients (29%) achieved ≥30% PSA decline with RT. In multivariate analyses with the IPTW method, the CSS and OS in the RT group were significantly longer than those in the non-RT group. In subgroup analyses with the IPTW method, RT was significantly associated with improved OS in patients aged ≥75 years and patients with initial PSA ≥500 ng/mL, cT4, Gleason score ≥8, high-volume metastatic burden. Conclusions RT to the primary tumor is safe and feasible, and it has potential benefits on oncological outcomes in patients with mCRPC.