Locoregional therapy for oligometastatic prostate cancer has generated great interest. However, its benefit for castration-resistant prostate cancer (CRPC) has not been fully demonstrated. Our objective was to evaluate the treatment outcome of progressive site-directed therapy (PSDT) for oligoprogressive CRPC (OP-CRPC).

This study cohort consisted of 101 patients with CRPC who underwent whole-body diffusion-weighted magnetic resonance imaging between 2014 and 2018, when a new line of anticancer therapy was being considered. For OP-CRPC, PSDT with radiation therapy and unchanged continuation of systemic therapy were recommended.

Thirty-eight patients received a diagnosis of OP-CRPC, and 23 (61%) underwent PSDT at a median prostate-specific antigen (PSA) level of 7.8 ng/mL. The regional radiation therapy targets were the prostate/pelvic lymph nodes (n = 7), bone (n = 15), or both (n = 1). A decrease in PSA levels of at least 50% in response to PSDT (50% PSA decline) was observed in 16 cases (70%); the median time to PSA progression was 8.7 months. Intrapelvic localization of progressive lesions was a significant predictor of time to PSA progression (hazard ratio, 6.6; P = .007) as well as volumes of abnormal signal intensity on whole-body diffusion-weighted magnetic resonance imaging (hazard ratio, 0.5; P = .045). A 50% PSA decline was achieved in 16 of the 18 patients with intrapelvic OP-CRPC (89%) and in none of the 5 patients with non-intrapelvic OP-CRPC (P < .001). Intrapelvic OP-CRPC had a significantly longer time to PSA progression than non-intrapelvic OP-CRPC (10.1 vs 4.8 months, P = .0014).

PSDT can be an effective treatment option for OP-CRPC. Progressive site localization was an important factor in good PSA response.