Occupational exposures and male breast cancer: A nested case-control study in the Nordic countries.

Male breast cancer (MBC) is a rare and understudied disease. There is limited evidence on association between environmental and occupational agents and MBC. Some similarities in risk factors may be shared with female breast cancer. We evaluated solvents, metals, exhaust gases and other agents in relation to MBC within the large Nordic Occupational Cancer Study (NOCCA).The study included 1469 MBC cases and 7345 controls from Finland, Iceland and Sweden, matched for the date of birth, sex and country. Cases were identified through national cancer registries. Data on occupation and other demographic indicators were collected from census records and population registries. Overall, 24 occupational exposures were assessed. Exposure estimates were assigned by linking job titles to job-exposure matrices (NOCCA-JEM). Odds ratios (OR) and 95% confidence intervals (95% CI) were estimated by using conditional logistic regression models.Significantly decreased overall OR was observed for physical workload (OR = 0.78, 95% CI 0.67-0.91). Protective effect of physical workload was stronger by increasing exposure level with significant dose-response relationship (p-trend<0.01). Non-significantly increased ORs were observed for trichloroethylene, iron, lead, chromium, welding fumes and wood dust, and decreased ORs for asbestos, silica dust and perchloroethylene. However, these results were not consistent across all analyses.The current study showed 20-25% protective effect for physical workload at work, while no strong evidence for other agents was observed.