Assessment of Clinicopathological Characteristics and Clinical Outcomes of Patients Who Developed Non-Muscle-Invasive Bladder Cancer After Radiotherapy for Prostate Cancer: A Retrospective Multicenter Study.

Radiotherapy for prostate cancer may induce the development of secondary bladder cancer. However, the clinicopathological characteristics and clinical outcomes of this entity have not been fully elucidated. Therefore, this study compared the clinicopathological characteristics and clinical outcomes of patients who developed secondary bladder cancer after radiotherapy with those of controls. The medical records of patients newly diagnosed with non-muscle-invasive bladder cancer were retrospectively analyzed. Newly diagnosed non-muscle-invasive bladder cancer that developed ≥ 5 years after radiotherapy for prostate cancer was defined as secondary non-muscle-invasive bladder cancer during this study. Patients with newly diagnosed non-muscle-invasive bladder cancer who did not meet this criterion were included in the control group. The clinicopathological characteristics and recurrence-free survival rates of patients with secondary non-muscle-invasive bladder cancer were compared with those of controls. A total of 26 (2.6%) of the 1,019 patients from the Tohoku Urological Evidence-Based Medicine Study Group and Kyoto University Hospital who were screened met this criterion for secondary non-muscle-invasive bladder cancer. Clinicopathological characteristics were similar between the secondary non-muscle-invasive bladder cancer and control groups, except for sex and age. Propensity score-matched analysis revealed that the recurrence-free survival rates of patients with secondary non-muscle-invasive bladder cancer may not be poorer than those of control patients. Tumor characteristics and recurrence-free survival rates of patients with secondary non-muscle invasive bladder cancer were comparable with those of controls. Further large-scale studies should be conducted to clarify the tumor characteristics and clinical outcomes of these patients after radiotherapy.