Enigmatic Differences by Sex in Cancer Incidence: Evidence From Childhood Cancers

We investigated the differences in cancer incidence between boys and girls. The incidence data for pediatric cancers were retrieved from the International Incidence of Childhood Cancer project (1990-2015). Poisson regression was applied to detect the sex differences in cancer incidence at global and regional levels. Boys were more susceptible to childhood cancers than girls, with a global boy-to-girl incidence rate ratio of 1.27 (95% confidence interval (CI): 1.26, 1.28) for leukemia, 1.48 (95% CI: 1.46, 1.51) for lymphomas, 1.10 (95% CI: 1.08, 1.11) for central nervous system neoplasms, 1.11 (95% CI: 1.08, 1.13) for neuroblastoma, 1.05 (95% CI: 1.02, 1.09) for retinoblastoma, and 1.39 (95% CI: 1.33, 1.45) for hepatic tumors. Incidence among girls was predominant only in renal tumors (incidence rate ratio = 0.90, 95% CI: 0.88, 0.92). Significant sex differences were observed in childhood cancers based on global-scale cancer data. The most pronounced disparities were observed mostly in developing countries, highlighting that data registration quality should be improved and that attention is needed for health-care access and service utilization for girls in these regions. Additionally, given the limited exposures to environmental risk factors in children, the differences might be mainly attributable to some endogenous risk factors and warrant further investigations.