Racial and ethnic differences in risk of second primary cancers among prostate cancer survivors

Purpose: Previous studies have shown an overall decreased risk of second cancers among prostate cancer survivors, but this has not been comprehensively examined by race/ethnicity. We conducted a retrospective cohort study of 716,319 one-year survivors of prostate cancer diagnosed at ages 35–84 during 2000–2015 as reported to 17 US Surveillance, Epidemiology and End Results (SEER) registries. Methods: We estimated standardized incidence ratios (SIRs) for second primary non-prostate malignancies by race/ethnicity (non-Latino white, Black, Asian/Pacific Islander [API] and Latino), by Gleason, and by time since prostate cancer diagnosis. Poisson regression models were used to test heterogeneity between groups with the expected number as the offset. Results: 60,707 second primary malignancies were observed. SIRs for all second cancers combined varied significantly by race/ethnicity: SIR: 0.88 (95% confidence interval: 0.87–0.89), SIR: 0.92 (0.89–0.95), SIR: 0.97 (0.95–0.99), and SIR: 1.05 (1.01–1.09) (p-heterogeneity < 0.001). SIRs for all cancers combined were higher among survivors of higher vs. lower Gleason prostate cancers irrespective of race/ethnicity. We observed significant heterogeneity by race/ethnicity in SIRs for 9 of 14 second cancer types investigated including lung, bladder, kidney, and liver. Conclusions: Our results confirm that most prostate cancer survivors have lower risks of second cancers than expected, but the magnitude varied by race/ethnicity. Exceptionally, API men had small but significantly increased risk. Further research to understand drivers of the observed race/ethnicity heterogeneity is warranted.