Sex ratio disparities in the two most common cancers worldwide: an exploratory analysis using GLOBOCAN 2022 data, gender inequalities, and economic indicators.

Background: Lung and colorectal cancers are the most common non-sex-specific cancers worldwide and represent a major share of global incidence and mortality. Although international variations in incidence are well documented, the contribution of structural gender inequalities and economic context to these disparities remains insufficiently explored. This study explores how gender inequalities and economic context relate to male-to-female incidence sex ratios of lung and colorectal cancers in a subset of 29 countries. Methods: We conducted an ecological analysis using GLOBOCAN 2022 data. The study included 29 countries with high-quality and comparable data on gender inequality, economic indicators, and cancer incidence. Associations between the Gender Inequality Index (GII), gross domestic product (GDP) per capita, and incidence sex ratios were examined using multivariable linear regression models. Sensitivity analyses were performed to assess robustness, including exclusion of influential countries and log-transformed models. Findings: Structural gender inequalities, measured by the GII, were strongly associated with higher male-to-female incidence sex ratios for lung cancer, and this relationship persisted after adjustment for smoking prevalence. This suggests that social and structural mechanisms beyond behavioural risk factors contribute to sex disparities in lung cancer incidence. For colorectal cancer, economic context was the principal determinant of sex differences in incidence, while associations with gender inequality were limited and variable. In more gender-equal, high-income countries, colorectal cancer incidence tended to converge between men and women, likely reflecting increasingly similar exposures and lifestyles. Interpretation: These findings highlight the importance of integrating structural gender inequalities and macroeconomic context into analyses of cancer incidence. Incorporating such social determinants alongside behavioural and biomedical risk factors may improve the relevance of prevention strategies and cancer surveillance efforts, particularly in high-income settings. However, these findings should be interpreted with caution given the ecological design of the study and the limited ability to account for all potential confounding or mediating factors. Funding: This project was funded by the Gender and Health Inequalities (GENDHI) project, ERC-2019-SyG grant agreement No. 856478.