Burden of cancer attributable to exogenous hormone use in Japan in 2015.

Exogenous female hormone use has not been as popular in Japan as in western populations. Here, we estimated the population-attributable fraction (PAF) of cancers in Japan in 2015 attributed to exogenous female hormone use. We used the most recent prevalence data for oral contraceptives (OC) and hormone replacement therapy (HRT), available from a large-scale population-based cohort study started in 2011-2016. For the purpose of this study, optimal usage of exogenous hormones was considered to be none. PAF was calculated for each age group using a standard formula. Overall, a negligible fraction, 0.4% of cancer incidence and 0.2% of cancer mortality in Japanese women was attributable to exogenous hormone use (OC use and HRT), and 0.2% of cancer incidence and 0.1% of cancer mortality overall when both sexes combined. The relatively low prevalence of exogenous hormone use in Japan compared to Western countries may explain the low fraction of cancer attributable to exogenous hormones among Japanese women.