Time to Oligoprogression From the Initiation of the Most Recent Systemic Treatment Is Associated With the Outcome of Progressive Site‐Directed Therapy for Castration‐Resistant Prostate Cancer

Objectives The efficacy of local therapy for oligometastatic prostate cancer has been increasingly reported; however, there is little evidence regarding the treatment of patients with castration‐resistant disease compared with that for those with castration‐sensitive disease. In this retrospective study, we examined data of patients with oligoprogressive castration‐resistant prostate cancer (CRPC) treated with progressive site‐directed therapy (PSDT) and investigated the prognosticators of treatment efficacy. Methods The cohort comprised 35 patients with oligoprogressive CRPC who underwent radiotherapy in the form of PSDT. Oligoprogression was defined as the presence of five or fewer affected sites. Radiation was administered to all lesions without interruption or modification of systemic therapy. The endpoints were prostate‐specific antigen (PSA) response, progression‐free survival (PFS), and cancer‐specific survival (CSS). Results The most common site was bone (57.1%), and the prostate was a site in 10 (28.6%) patients. Twenty patients (57.1%) achieved a PSA response of ≥ 50%. The median PFS and CSS were 8.0 months (95% confidence interval [CI], 2.3–22.8) and 28.7 months (95% CI, 17.6–not reached), respectively. Multivariate analysis identified time to oligoprogression from the initiation of the most recent systemic treatment ≥ 1 year as a favorable prognostic factor of PFS (hazard ratio [HR], 0.35; 95% CI, 0.13–0.94; p = 0.038). One patient (2.9%) developed urinary frequency (Grade 2). Conclusions PSDT for oligoprogressive CRPC may achieve good disease control in patients who evidenced time to oligoprogression ≥ 1 year after the initiation of the most recent systemic treatment.