Breast cancer and occupational exposures in women in Finland

Background: The etiology of breast cancer is not fully under-stood. Environ mental and occupational exposures may contribute to breast cancer risk. Methods: We linked 324 job titles from the 1970 census of 892,591 Finnish w omen with incidence of breast cancer (23,638 cases) during 1971-1995. We co nverted job titles to 31 chemical and two ergonomic agents through a measur ement-based, period-specific, national job-exposure matrix. Poisson regress ion models were fit to the data, with adjustment for birth cohort, follow-u p period, socioeconomic status, mean number of children, mean age at first delivery, and turnover rate. Results: For premenopausal breast cancer;. medium/high level of occupationa l exposure to ionizing:radiation was; associated with a standardized incide nce ratio (SIR) of 1.3 (95% confidence interval (CI) 0.7-2.5; trend P = 0.0 3). For postmenopausal breast cancel; we found art SIR of 1.2 (1.1-1.3)for low level and 1.4 (1.1-1.8)for medium/high level of ionizing radiation (tre nd P = 0.001); and an SIR 1.3 (1.1-1.7)for medium/high levels of both asbes tos and map-made vitreous fibers. Aromatic hydrocarbon solvents showed a si gnificant trend for a modest excess of postmenopausal breast cancer. Conclusions:Our study indicates that occupational exposure to ionizing radi ation may be associated with an increased risk of female breast cancer High -quality studies on environmental and occupational etiology of breast cance r are needed for further elucidation of risk factors.:Am. J. Ind. Med. 36:4 8-53, 1999. (C) 1999 Wiley-Liss, Inc.