External beam radiotherapy combination is a risk factor for bladder cancer in patients with prostate cancer treated with brachytherapy

PurposeTo investigate the risk of bladder cancer (BCa) in patients treated with brachytherapy for prostate cancer (PCa).MethodsWe retrospectively analyzed 583 patients with PCa who underwent brachytherapy with or without external beam radiotherapy (EBRT). We analyzed the disease-free survival (DFS) of BCa in patients with PCa who underwent brachytherapy with or without EBRT. We performed multivariate Cox regression analyses of DFS using age, EBRT, and Brinkman index (BI) score (number of cigarettes smoked per day x number of years smoking) >= 200 as variables for BCa after brachytherapy.ResultsFourteen patients (2.4%) developed BCa after brachytherapy with or without EBRT. The percentage of high-grade urothelial carcinoma (UC) was 63.6%. A total of 85.7% of patients had non-muscle invasive BCa, and 14.3% of patients had muscle invasive BCa. DFS was longer in brachytherapy monotherapy than in combination therapy (brachytherapy + EBRT). Multivariate Cox regression analysis showed that a BI score >= 200 (Hazard Ratio (HR 8.61; 95% Confidence Interval (CI) 1.12-65.98) and EBRT combination (HR 3.29; 95% CI 1.03-10.52) were significantly associated with BCa development in patients with PCa treated with brachytherapy. Furthermore, patients with BI score >= 200 and EBRT combination had a significantly higher risk of BCa compared with patients with BI score < 200 (HR Log-rank test P = 0.010).ConclusionMost cases of BCa after brachytherapy with or without EBRT are high grade and invasive. We hypothesized that the EBRT combination might be a risk factor for BCa in patients with PCa who underwent brachytherapy.