Variability of Sex Disparities in Cancer Incidence over 30 Years: The Striking Case of Kidney Cancer.

It is well established that men are at higher risk of most non-sex-specific cancers than women, but there has been surprisingly little research investigating these differences. This is possibly because differences in exposure to established risk factors and hypothesised protection by female sex hormones are thought to account for the totality of the sex differences. These explanations remain somewhat speculative, as the magnitude of the sex ratio in cancer incidence has not been systematically studied, with no quantitative estimate of the variability of the sex ratio across countries, age groups, and periods of diagnosis. We analysed worldwide cancer incidence data for the years 1978-2007 in terms of sex disparities, and explicitly quantified the variability in sex disparities by age, year, and geographical region. Our analysis highlights several cancer types for which suspected and commonly accepted factors are unlikely to fully explain the observed sex disparity. In particular, kidney cancer showed a 2:1 male/female case incidence ratio that was constant by age, year, and region, suggesting that factors other than sociocultural habits and health behaviours are responsible for this sex disparity. PATIENT SUMMARY: We quantified the difference in the incidence of various cancer types between men and women across the world over 30 years. While the trends for some cancers such as lung cancer are clearly correlated with known variations in lifestyle habits, we found that the sex disparity observed for others such as kidney cancer is unlikely to be explained by known risk factors.