Sex differences in cancer incidence persist across race and ethnicity

BACKGROUND: Males have a higher incidence of cancers at shared anatomic sites than females. We investigated whether sex differences in cancer incidence differed across race/ethnicity. METHODS: Within the Multiethnic Cohort Study, we examined the association between sex and cancer incidence at 13 shared anatomic sites using Cox proportional hazards regression to estimate male-to-female hazard ratios (MF HRs) adjusting for cancer specific risk factors by race/ethnic group: African American, Japanese American, Native Hawaiian, Latino, and White. Statistical differences in the MF HRs by race/ethnicity for each site were assessed with an interaction term. The percentage of sex difference in cancer incidence that was statistically explained by the risk factors within race/ethnicity were quantified using a Peters-Belson approach. RESULTS: Of the 178,036 participants, 46% were male and 54% were female. Adjusting for multiple risk factors did not eliminate the MF differences for any of the cancers examined. We found significant differences in MF HRs across race/ethnicity for cancers of the esophagus (Native Hawaiian MF HR 17.67, 95% CI 2.21-141.20; African American 1.28 0.69-2.36; P = 0.018), liver (Japanese American 1.28, 0.96-1.70; White 2.79, 1.81-4.30, P = 0.005) and thyroid (Latino 0.21, 0.13-0.35; White 0.83, 0.50-1.37, P = 0.005). Cancer risk factors explained 82% of the overall sex difference observed for lung cancer but 0% of the difference for gallbladder cancer. DISCUSSION: Most non-sex-specific cancers have male predominance across race/ethnicity, which are not fully explained by cancer risk factors, suggesting there may be intrinsic sex differences driving these differences in cancer incidence.