Differences in incidence and clinicopathologic features of secondary bladder cancer after long-term follow-up of brachytherapy and radical prostatectomy for localized prostate cancer.

381 Background: Although there studies have been reported that brachytherapy (BT) for prostate cancer is associated with an increased incidence of metachronous urinary bladder cancer (MBC), few studies have clarified differences in the clinicopathological features (CPF) of MBC between BT and prostatectomy (RP). We studied the risk and clinicopathological CPF of MBC between RP and BT groups in our hospital after long-term follow-up. Methods: Five hundred four patients treated with BT and 471 referred patients treated with RP between 2006 and 2017 in our hospital were reviewed. We compared the incidence of MBC and the CPF including the tumor number, location within the bladder, histology, and time from BT or RP to the MBC occurrence between BT and RP. The differences between the two groups were analyzed. Furthermore, in the BT group, the radiation dose distribution within bladder was estimated. Results: A total of 11 cases of MBC occurred in the BT group (2.2%) and 7 in the RP group (1.5%) after a median follow-up time of 107 months (13-209). The median time from initial treatments to the occurrences of MBC was 65 months (12-121) in BT and 100 months (4-126) in RP (p=0.469). Average tumor number was not significantly different between the groups (BT:1.4, RP:1.9, p=0.589). The tumor locations of MBC within the bladder for BT vs. RP were 9 vs. 1 in the lateral wall, 0 vs. 4 in the posterior wall, 0 vs. 3 in the dome, and 1 vs. 0 in the trigone. The incidence in the lateral wall was significantly higher in BT than in RP (p=0.001). Their median radiation dose of right wall (15.7±7.74Gy) and left wall (13.0±5.85Gy) showed no significant difference compared to the BT patients without MBC. There were 3 muscle-invasive cases in BT and 1 in RP (p=0.60). High-grade urothelial carcinoma occurred significantly more in BT (10 cases) than in RP (1 case) (p=0.001). According to the criteria, six MBC were judged as radiation-induced secondary bladder cancer. Conclusions: Long-term follow-up showed that the risk of MBC after BT was similar to that after RP. MBC after BT occurred significantly more frequently in the lateral wall and had a higher grade compared to those after RP.