Mortality rates in radical cystectomy patients with bladder cancer after radiation therapy for prostate cancer.

Objective: To conduct a population-based study examining cancer-specific mortality (CSM) and other-cause mortality (OCM) differences in patients with radiation-induced secondary bladder cancer (RT-BCa) vs those with primary bladder cancer (pBCa) undergoing radical cystectomy (RC).

Methods: Within the Surveillance, Epidemiology, and End Results database (2004-2020), we identified patients with T_2-4N_0-3M₀ bladder cancer treated with RC, who had previously been treated with external beam radiation therapy (EBRT) or brachytherapy for prostate cancer, as well as patients with T_2-4N_0-3M₀ pBCa treated with RC. Cumulative incidence plots and multivariable competing risks regression (CRR) models were used to assess CSM after additional adjustment for OCM. The same methodology was then repeated based on organ-confined (OC: T₂N₀M₀) and non-organ-confined (NOC: T_3-4 and/or N_1-3) disease.

Results: Of 9957 RC patients, RT-BCa was identified in 347 (3%) compared with 9610 (97%) who had pBCa. In multivariable CRR models, no CSM differences were recorded in the overall comparison (P = 0.8), nor in sub-groups based on OC and NOC disease (P = 0.8 and 0.7, respectively). Conversely, multivariable CRR models identified RT-BCa as an independent predictor of 1.3-fold higher OCM in the overall cohort and of 1.5-fold higher OCM in those with NOC disease. In a sensitivity analysis of patients with NOC disease, EBRT was associated with higher OCM rates (hazard ratio 1.5). By contrast, OCM rates were not different in those with OC disease (P = 0.8).

Conclusion: Our study showed that RC for RT-BCa was associated with similar CSM rates as RC for pBCa, regardless of disease stage. However, patients who had undergone EBRT exhibited significantly higher OCM in the NOC sub-group.