Garcia E, et al. – This study analyzed the link between exposure to metalworking fluid (MWF) and incidence of breast cancer among a cohort of female autoworkers. In separate analyses of premenopausal breast cancer, defined by age at diagnosis, it was observed that the hazard ratios (HR) for incident breast cancer were elevated for exposure to synthetic MWF, chemical lubricants with no oil content, possibly indicating a different mechanism for the younger cases. Findings add to the limited literature about quantitative chemical exposures and breast cancer risk.