Salvage radiotherapy after radical prostatectomy in a Japanese cohort: Analysis from the MICAN study.

342 Background: The clinical benefit of salvage radiotherapy (SRT) for biochemical recurrence (BCR) after radical prostatectomy (RP) remains controversial, particularly regarding patient selection. We evaluated the impact of SRT on oncologic outcomes in a large Japanese cohort using the MICAN registry. Methods: The MICAN study is a multicenter retrospective registry of patients who underwent RP between 2010 and 2020 in Japan. Among 3,463 cases, we identified 610 patients who experienced postoperative PSA recurrence, had no prior neoadjuvant therapy, and were pN0 or pNx. These were divided into those who received SRT (Group A, n=308) and those who did not (Group B, n=302). SRT was delivered to the prostate bed at 60–72 Gy. Primary endpoints were overall survival (OS) and androgen deprivation therapy-free survival (ADT-FS). Multivariate analysis was conducted using Cox proportional hazards models. Results: Median PSA recurrence-free survival was comparable (19.3 vs 19.1 months; P=0.132). Group A was significantly younger (67 vs 70 years; P<0.001) and had a higher rate of positive surgical margins (51.8% vs 44.1%; P=0.036). Ten-year OS was not significantly different overall (93.6% vs 89.9%; P=0.285), but SRT significantly improved OS in patients with positive margins (97.3% vs 84.0%; P=0.007). No OS benefit was observed among patients with negative margins. pGG was the only independent predictor of OS in multivariate analysis. However, SRT significantly prolonged ADT-FS (10-year: 55.3% vs 37.1%; P<0.001), and both pGG and SRT remained significant in multivariate analysis. Conclusions: In this Japanese multi-institutional cohort, SRT significantly improved ADT-free survival after PSA recurrence, with a survival benefit observed specifically in patients with both positive surgical margins and high-grade disease (pGG 4–5).