Chemical exposures in the workplace and breast cancer risk: A prospective cohort study.

We investigated the relationship between workplace chemical exposures and breast cancer risk among women enrolled in the Sister Study, a prospective cohort study of US and Puerto Rican women. A total of 47,640 participants reported work outside of the home. Workplace exposure to eleven agents (acids, dyes or inks, gasoline or other petroleum products, glues or adhesives, lubricating oils, metals, paints, pesticides, soldering materials, solvents and stains or varnishes) was characterized based on self-reports of frequency and duration of use. Approximately 14% of the study population reported exposure to only one agent and 11% reported working with two or more of the 11 agents in their lifetime. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated for each agent, adjusting for established breast cancer risk factors. During follow-up, 1,966 cases of breast cancer were reported. Although there were no significant associations between ever use of the eleven agents evaluated and breast cancer risk, women with cumulative exposure to gasoline or petroleum products at or above the highest quartile cutoff had an elevated risk of total (HR: 2.3, 95%CI: 1.1-4.9) and invasive (HR: 2.5, 95%CI: 1.1-5.9) breast cancer compared with women in the lowest quartile group (ptrend  = 0.03). Workplace exposure to soldering materials was associated with an increased risk of premenopausal breast cancer (HR = 1.8, 95% CI = 1.1-3.0). Findings support the need for further studies to elucidate the role of occupational chemicals in breast cancer etiology.