Occupational class and male cancer incidence: Nationwide, multicenter, hospital-based case-control study in Japan

Little is known about socioeconomic inequalities in male cancer incidence in nonwestern settings. Using the nationwide clinical and occupational inpatient data (1984-2016) in Japan, we performed a multicentered, matched case-control study with 214 123 male cancer cases and 1 026 247 inpatient controls. Based on the standardized national classifications, we grouped patients' longest-held occupational class (blue-collar, service, professional, manager), cross-classified by industrial cluster (blue-collar, service, white-collar). Using blue-collar workers in blue-collar industries as the referent group, odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by conditional logistic regression with multiple imputation, matched for age, admission date, and admitting hospital. Smoking and alcohol consumption were additionally adjusted. Across all industries, a reduced risk with higher occupational class (professionals and managers) was observed for stomach and lung cancer. Even after controlling for smoking and alcohol consumption, the reduced odds persisted: OR of managers in white-collar industries was 0.80 (95% CI 0.72-0.90) for stomach cancer, and OR of managers in white-collar industries was 0.66 (95% CI 0.55-0.79) for lung cancer. In white-collar industries, higher occupational class men tended to have lower a reduced risk for most common types of cancer, with the exception of professionals who showed an excess risk for prostate cancer. We documented socioeconomic inequalities in male cancer incidence in Japan, which could not be explained by smoking and alcohol consumption.