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

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.

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.

60,707 second primary malignancies were observed. SIRs for all second cancers combined varied significantly by race/ethnicity: SIR_white: 0.88 (95% confidence interval: 0.87-0.89), SIR_Latino: 0.92 (0.89-0.95), SIR_Black: 0.97 (0.95-0.99), and SIR_API: 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.

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.