Bladder cancer risk following primary and adjuvant external beam radiation for prostate cancer

PURPOSE: Increased rates of secondary bladder malignancies have been reported after external beam radiation therapy (EBRT) for gynecological malignancies with relative risks of 2 to 4. This study was designed to determine if there was an increase in bladder cancer after EBRT for prostate cancer. MATERIALS AND METHODS: We retrospectively reviewed the Mayo Clinic Cancer Registry for patients who received EBRT for prostate cancer (1980 to 1998). Patients diagnosed with bladder cancer were identified. Comparative incidence rates were obtained from the national Surveillance, Epidemiology and End Results database. Subset analysis included patients treated with adjuvant radiation and those residing locally. Medical histories of patients with bladder cancer were reviewed. RESULTS: A total of 1,743 patients received EBRT for prostate cancer at our institution. In more than 12,353 man-years of followup no increase in bladder cancer risk was encountered. Subset analysis of men who received adjuvant radiation demonstrated that the relative risk of bladder cancer was increased but was not statistically significant. When the analysis was restricted to patients residing in the local area, the number of patients in whom subsequent bladder cancer developed was similar to Surveillance, Epidemiology and End Results rates. However, in the adjuvant radiation subset there was a statistically significant increase in subsequent bladder cancer. Patients in whom bladder cancer develops after EBRT often present with low grade disease but many have recurrence and progression. CONCLUSIONS: This retrospective review suggests there is not evidence of increased risk of bladder cancer after radiation therapy, assuming unbiased followup and complete ascertainment of cases. The natural history of bladder cancer in this population does not seem to be altered by a history of radiation.