Smoking effect on secondary bladder cancer after external beam radiotherapy for prostate cancer

Objective: Although it is well known that radiotherapy for prostate cancer increases comorbid rate of secondary bladder cancer, the effect of aging and smoking with radiotherapy on incidence rate of secondary bladder cancer remains unknown. Then, this study investigated the combinational effect of external beam radiotherapy for prostate cancer and aging or smoking on comorbid rate of secondary bladder cancer.Methods: This study included 754 Japanese patients with prostate cancer treated with radiotherapy (n = 319) and radical prostatectomy (n = 435) from 2000 through 2013. The relationship between therapeutic modality for prostate cancer as well as age or smoking status and comorbid rate of secondary bladder cancer was examined.Results: During the median follow-up period of 4.3 and 3.1 years, secondary bladder cancer occurred in 11 (3.4%) and 5 (1.1%) of patients with prostate cancer treated with external beam radiotherapy and radical prostatectomy, respectively. The 5-year bladder cancer-free survival rate was 97.3% in the external beam radiotherapy group and 99.4% in the radical prostatectomy group. Age (hazard ratio = 1.15, P = 0.027) and ever smoking (hazard ratio = 5.65, P = 0.011) were significant predictive factors of secondary bladder cancer incidence in the external beam radiotherapy cohort, but not in the radical prostatectomy cohort. Inversely, among men with ever smoking, but not among older men, external beam radiotherapy (hazard ratio = 9.64, P = 0.0052) was a significant risk factor of secondary bladder cancer.Conclusions: Taken together, these findings suggest that smoking history might be one of criteria to choose radical prostatectomy than external beam radiotherapy for prostate cancer, and that age would not be a criterion for therapeutic selection in terms of secondary bladder cancer.