Introduction The etiology of breast cancer is only partially understood. An increasing body of epidemiological evidence indicates that environmental and occupational factors may affect breast cancer risk, yet no established risk factors have been identified. Although recent studies have shown increased risks associated with specific workplace exposures, the evidence remains largely inconclusive for most occupational agents.

Objectives To examine associations between selected occupational exposures and breast cancer risk.

Methods In a population-based case-control study conducted in France between 2005 and 2008, detailed information on lifetime occupational history was collected for 1,206 cases and 1,294 population controls. An industrial hygienist coded occupations and industries for each job held by a participant. To identify occupational exposures, job codes were linked to the Canadian job-exposure matrix. Twenty-seven agents with relatively high prevalence were selected. Three exposure metrics of ever exposure, duration of exposure, and cumulative exposure to selected agents were analyzed. The reference group were participants having never been exposed to the specific agent. Odds ratios (OR) and 95% confidence intervals for associations with breast cancer were estimated using logistic regression models, adjusting for well-established breast cancer risk factors.

Results Increased risks were suggested for high cumulative exposure to calcium carbonate, polyester fibres, fabric dust, cotton dust, aliphatic aldehydes, mononuclear aromatic hydrocarbons, and synthetic adhesives, with ORs ranging from 1.45 to 1.66. Inverse associations were observed for all exposure metrics for ultraviolet radiation and grain dust, with ORs ranging from 0.41 to 0.68.

Conclusion These findings suggest that some occupational exposures may increase breast cancer risk. The decreased ORs associated with ultraviolet radiation and grain dust suggest that certain exposures that are typical of agricultural workers might be protective but should be interpreted with care. More research contributing to the knowledge base on occupational factors in relation to breast cancer is required.