Rates of Secondary Bladder and Rectal Cancers After External Beam Radiation for Prostate Cancer According to Age and...

External beam radiation therapy (EBRT) predisposes to radiation-induced bladder (BCa) and/or rectal cancer (RCa). This risk may have declined with modern radiation techniques. Moreover, it remains unclear whether the risk varies by age or D'Amico risk classification.

Within the Surveillance, Epidemiology, and End Results database (2004-2020), we identified patients who were treated with either EBRT or radical prostatectomy (RP) for prostate cancer. Cumulative incidence plots and competing risks regression (CRR) models were fitted. Subgroup analyses were performed according to year of diagnosis (contemporary: 2012-2020 vs. historical: 2004-2011 cohorts), age (< 65 vs. ≥ 65) and D'Amico risk groups.

Of 251,838, 110,239 (44%) underwent EBRT versus 141,599 RP (56%). Relative to RP patients, EBRT was associated with a two-fold higher 10-year incidence of secondary BCa (0.9 versus 1.9%, respectively). In multivariable CRR models, EBRT was associated with higher risk of BCa (HR: 1.5, 95% CI: 1.3-1.6, P < .001). Similarly, relative to RP, EBRT was also associated with two-fold higher 10-year incidence of secondary RCa (0.8 versus 1.5%, respectively). In multivariable CRR models, EBRT was associated with higher risk of RCa (HR: 1.4, 95% CI: 1.2-1.5, P < .001). In subgroup analyses, the 5-year EBRT-RP absolute difference in secondary RCa was lower in the contemporary cohort (0.2%) than in the historical cohort (0.5%), whereas no such reduction was observed for BCa. In subgroup analyses according to D'Amico risk groups and age, no clinically significant differences were recorded.

EBRT is associated with higher risk of both BCa and RCa as compared to RP. In contemporary EBRT patients, secondary RCa rate is lower, but not BCa rate. D'Amico risk groups as well as age categories did not affect either secondary BCa or secondary RCa rates.