Racial differences in the risk of second primary bladder cancer following radiation therapy among localized prostate cancer patients.

Objectives: To investigate the race-specific second primary bladder cancer (SPBC) risk following prostatic irradiation.

Methods: Louisiana residents who were diagnosed with localized prostate cancer (PCa) in 1996-2013 and received surgery or radiation were included. Patients were followed until SPBC diagnosis, death, or Dec. 2018. The exposure variable was type of treatment (radiation only vs. surgery only). The outcome was time from PCa diagnosis to SPBC diagnosis, stratified by race. Fine and Gray's competing risk model was applied with death as a competing event and adjustment of sociodemographic and tumor characteristics. We used 5 years and 10 years as lag time in the analyses.

Results: A total of 26,277 PCa patients with a median follow-up of 10.7 years were analyzed, including 18,598 white and 7679 black patients. About 42.9 % of whites and 45.7 % of blacks received radiation. SPBC counted for 1.84 % in the radiation group and 0.90 % in the surgery group among white patients and for 0.91 % and 0.58 %, respectively, among black patients. The adjusted subdistribution hazard ratio of SPBC was 1.80 (95 % CI: 1.30-2.48) for radiation recipients compared to surgery recipients among white patients; 1.93 (95 % CI: 1.36-2.74) if restricted to external beam radiation therapy (EBRT). The SPBC risk was not significantly different between irradiated and surgically treated among blacks.

Conclusions: The SPBC risk is almost two-fold among white irradiated PCa patients compared to their counterparts treated surgically. Our findings highlight the need for enhanced surveillance for white PCa survivors receiving radiotherapy, especially those received EBRT.