Does Race/Ethnicity Affect Secondary Bladder and Rectal Cancer Rates After Prostate Cancer Radiation? Results from a Population-Based Study.

Background: It is unknown whether race/ethnicity affects the risk of secondary bladder cancer (BCa) or rectal cancer (RCa) after external beam radiation therapy (EBRT) or brachytherapy (BT) for prostate cancer (PCa).

Materials And Methods: Within the Surveillance, Epidemiology, and End Results database (2004-2020), we focused on Caucasians, Hispanics, African Americans (AAs), and Asian/Pacific Islanders (APIs). Cumulative incidence plots and competing risks regression (CRR) models were fitted. We tested for secondary BCa and RCa rates after either EBRT or BT relative to radical prostatectomy (RP) patients, in whom no radiation therapy was used. Additionally, we performed an interaction analysis to assess whether the effect of radiation therapy on secondary malignancy risk differed across racial groups.

Results: Of 285,859 patients, 202,421 (71%) were Caucasians, 41,719 (15%) AAs, 26,705 (9%) Hispanics, and 15,014 (5%) APIs. After EBRT, secondary BCa increase was HR 1.4 in Caucasians, HR 1.7 in AAs, HR 2.1 in APIs, and HR 2.2 in Hispanics relative to radiation-unexposed RP patients. Similarly, after BT, secondary BCa increase was HR 1.5 in Caucasians, HR 1.7 in AAs, HR 2.3 in APIs, and HR 2.4 in Hispanics. Regarding RCa, after EBRT, secondary RCa increase was HR 1.5 in Caucasians and HR 1.3 in both AAs and Hispanics. Similarly, after BT, relative secondary RCa increase was HR 1.4 in Caucasians and HR 1.5 in both AAs and Hispanics. No increase was recorded in APIs after EBRT (p = 0.09) either BT (p = 0.7). Finally, the interaction analysis were inconclusive whether the relative effect of EBRT/BT differ between races, while it suggested a baseline difference in the risk of secondary tumor between Caucasian and non-Caucasian race/ethnicities.

Conclusion: Radiation exposure does not result in major differences dictated by race or ethnicity when secondary BCa and RCa are considered, as the relative risk increase appears consistent across racial groups. Conversely, it appears that baseline risk (independent of radiation therapy) is inherently lower in non-Caucasian populations.