O-181 Occupational exposure to extremely low-frequency magnetic fields and postmenopausal breast cancer risk

IntroductionThe International Agency for Research on Cancer has classified Extremely Low-Frequency Magnetic Fields (ELF-MF) as possibly carcinogenic to humans but the literature on occupational exposure to ELF-MF and breast cancer risk is sparse.Material and MethodsIn this population-based case-control study, incident cases of histologically confirmed postmenopausal breast cancer were identified at 18 hospitals in Montreal, Canada, 2008–2011. Population controls comprised women without a history of breast cancer, randomly selected from the electoral list for Montreal, and frequency-matched to cases using 5-year age groups. We elicited information on occupational history and potential risk factors. An occupational hygienist coded all jobs to the International Standard Classification of Occupations 1988 (ISCO88); these occupation codes were linked to an ELF-MF job exposure matrix (JEM) to obtain mean workday-average ELF-MF exposure. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) for incident breast cancer and past ELF-MF cumulative exposure (CE) and average exposure (AE), adjusting for individual-level and ecological covariates. Separate analyses were conducted restricting exposure before the first full-term pregnancy or age 35 for women who were never pregnant and for hormonal receptor phenotypes.ResultsWe recruited 592 controls and 663 cases. The fully adjusted ORs per increase in the interquartile range (IQR=2.12 μT-years) of CE was 0.99 (95% CI: 0.94–1.06) and for AE (IQR=1.54 μT) was 0.96 (95% CI: 0.90–1.02). The associations between breast cancer and ELF-MF CE and AE were consistent with linearity. Adjustments for various combinations of potential confounders did not change these patterns. We found no evidence of associations for different breast cancer subtypes or exposure before the first full-term pregnancy or the age of 35.ConclusionsOur findings suggest that occupational exposure to ELF-MF, assigned here using a JEM, may not be associated with the risk of incident postmenopausal breast cancer.