Sex Differences in Cancer Incidence Rates by Race and Ethnicity: Results from the Surveillance, Epidemiology, and End Results (SEER) Registry (2000-2019)

While males exhibit higher incidence and mortality rates for most non-sex-specific cancers compared to females, the reasons behind these differences remain unclear. By analyzing the male-to-female rate ratios (MF IRRs) of non-sex-specific cancers by race and ethnicity, this research aims to shed light on whether sex-based differences are rooted in intrinsic biological variations or environmental exposures. Similarities of MF IRRs across race and ethnicity may suggest underlying biological variations that drive sex differences, while variations in MF IRRs may point to external factors driving these incidence differences. The results may help us understand the etiology of non-sex-specific cancers and the complex interplay between biology and environment in cancer development. Men have 2-3 times the rate of most non-sex-specific cancers compared to women, but whether this is due to differences in biological or environmental factors remains poorly understood. This study investigated sex differences in cancer incidence by race and ethnicity. Cancer incidence data from the Surveillance, Epidemiology, and End Result (SEER) program (2000-2019) were used to calculate male-to-female incidence rate ratios (MF IRRs) for each cancer site, stratified by race and ethnicity, and age-standardized to the 2000 U.S. population for individuals ages >= 20 years. Among 49 cancer sites, 44 showed male predominance (MF IRR > 1), with seven inconsistencies across race and ethnicity, including cancers of the lip, tongue, hypopharynx, retroperitoneum, larynx, pleura cancers, and Kaposi sarcoma. Four cancers exhibited a female predominance (MF IRR < 1), with only gallbladder and anus cancers varying by race and ethnicity. The MF IRRs for cancer of the cranial nerves and other nervous system malignancies showed no sex differences and were consistent (MF IRR = 1) across race and ethnicity. The MF IRRs for most cancers were consistent across race and ethnicity, implying that biological etiologies are driving the observed sex difference. The lack of MF IRR variability by race and ethnicity suggests a minimal impact of environmental exposure on sex differences in cancer incidence. Further research is needed to identify biological drivers of sex differences in cancer etiology.