Background Breast cancer is the leading cause of cancer death in women worldwide. Besides reproductive and hormonal breast cancer risk factors which are hardly modifiable, the identification of occupational or environmental risk factors may be a key to prevention. It has been suggested that exposure to organic solvents in the workplace may play a role in the etiology of breast cancer. However, most epidemiological studies on solvents in female breast cancer have reported inconsistent results.

Methods We examined the risk of breast cancer related to lifetime exposure to chlorinated, petroleum-based and oxygenated solvents in the CECILE study, a large population-based case-control study carried out in France (2005–2007). 1230 women with breast cancer and 1315 population controls were included. Data collected included sociodemographic characteristics, medical and family history, anthropometric measurements, reproductive history, lifestyle habits, and lifetime occupational history. All jobs were coded using the International Standard Classification of Occupations (ISCO 1968) and the Classification of Activities in the European Community (NACE 1991). Exposure to five chlorinated, five petroleum and five oxygenated solvents was assessed using job-exposure matrices, which assigned indices of exposure (probability, frequency and intensity) for each job. A Cumulative Exposure Score (CES) taking into account probability, frequency, intensity and duration of exposure was calculated for each subject. Odds ratio (ORs) and their 95% confidence intervals (95% CI) were estimated using unconditional logistic regression adjusting for potential confounders. Analyses were stratified by the menopausal status.

Results Significantly increased ORs were found in premenopausal women with high probability of exposure to alcohols (1.50; 1.05–2.14) and diethyl ether (1.97; 1.00–3.88). Premenopausal women with the highest CES of oxygenated solvents had an OR of 1.70 (1.09–2.64) (OR=1.67; 1.10–2.52 for alcohols, 1.80; 0.95–3.42 for diethyl ether); the highest CES of chlorinated solvents was associated with an OR of 2.14 (0.86–5.30). In premenopausal women, a duration of exposure to oxygenated solvents ≥25 years with a probability of exposure ≥80% significantly increased the risk of breast cancer (OR=2.62; 1.27–5.40 for all solvents, 2.72; 1.30–5.70 for alcohols, and 2.79; 0.67–11.6 for diethyl ether). No association was observed for oxygenated, petroleum-based or chlorinated solvents in postmenopausal women.

Conclusion These findings suggest a role of occupational exposure to oxygenated solvents, notably to alcohols and diethyl ether, in the occurrence of breast cancer in premenopausal women. Our results highlight the importance of timing and duration of exposure for the study of occupational exposure to solvents in breast cancer risk.