Residential and occupational exposures to 50-Hz magnetic fields and breast cancer in women: a population-based study.

A case-control study was conducted to investigate whether residential and occupational exposures to magnetic fields increased the risk for breast cancer among women. Cases of breast cancer diagnosed during 1980-1996 were identified in a cohort of women living near a high-voltage power line in Norway in 1980 or between 1986 and 1996. Each case was matched by year of birth, municipality, and first year of entry into the cohort with two randomly selected controls without cancer. Residential exposure to magnetic fields was calculated as that generated by the lines before diagnosis, and occupational exposure was based on exposure matrix data. Women with residential exposure had an odds ratio of 1.58 (95% confidence interval (CI): 1.30, 1.92) when compared with unexposed women. The odds ratios for exposed women versus unexposed women with estrogen receptor (ER)-positive and ER-negative breast cancer were 1.33 (95% CI: 0.93, 1.90) and 1.40 (95% CI: 0.78, 2.50), respectively (ER status was available for 44% of the cases). Women with the highest occupational exposure had an odds ratio of 1.13 (95% CI: 0.91, 1.40) when compared with those unexposed at work. The findings suggest an association between exposure to magnetic fields and breast cancer in women.