Investigating the risk of breast cancer among women exposed to chemicals: a nested case-control study using improved exposure estimates

Purpose The aim of this study was to examine if exposures to chemicals at the workplace were associated with an increased risk of postmenopausal breast cancer, using improved exposure estimates. Methods The design is a case-control study, nested within a cohort of women from the Malmo Diet and Cancer Study. The study comprised 2400 women, 731 cases and 1669 matched controls, born 1923-1950 and living in Malmo, Sweden between 1991 and 1996. An occupational hygienist reclassified the probability for exposure given by a job-exposure matrix, using individual data on work tasks. First-time diagnoses of invasive breast cancer were identified through the Swedish Cancer Registry. Results Women exposed to chemicals in their occupational environment had a statistically significantly increased risk (OR 1.59, 95% CI 1.11-2.29) of breast cancer, and the risk correlated positively with duration of exposure but not with exposure intensity. Women exposed to chlorinated hydrocarbon solvents for more than 10 years had a significant higher risk of breast cancer (OR 3.06, 95% CI 1.18-7.96) as well as women exposed to oil mist for more than 10 years (OR 3.08, 95% CI 1.12-8.49). Conclusions This study gives some support to the hypothesis that exposure to organic solvents as well as oil mist is associated with increased risk of breast cancer.