The This study estimated the cancer burden attributable to modifiable factors in Japan in 2015 using the best available epidemiological evidence and a standard methodology. We selected the following factors for inclusion in the estimates, namely tobacco smoking (active smoking and secondhand smoking), alcohol drinking, excess bodyweight, physical inactivity, infectious agents (Helicobacter pylori, hepatitis C virus, hepatitis B virus, human papilloma virus, Epstein-Barr virus, and human T-cell leukemia virus type 1), dietary intake (highly salted food, fruit, vegetables, dietary fiber, red meat, processed meat), exogenous hormone use, never breastfeeding and air pollution, given that these were considered modifiable, in theory at least. We first estimated the population attributable fraction (PAF) of each cancer attributable to these factors using representative relative risks of Japanese and the prevalence of exposures in Japanese around 2005, in consideration of the 10-year interval between exposure and cancer outcomes. Using nationwide cancer incidence and mortality statistics, we then estimated the attributable cancer incidence and mortality in 2015. We finally obtained the PAF for site-specific and total cancers attributable to all modifiable risk factors using this formula, with statistical consideration of the effect of overlap between risk factors. The results showed that 35.9% of all cancer incidence (43.4% in men and 25.3% in women) and 41.0% of all cancer mortality (49.7% in men and 26.8% in women) would be considered preventable by avoidance of these exposures. Infections and active smoking followed by alcohol drinking were the greatest contributing factors to cancer in Japan in 2015.
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