Recent epidemiologic evidence suggests that occupational exposures to electromagnetic fields and light at night, from working night and/or rotating shifts, may increase female breast cancer risk. Suppression of melatonin by EMF and light at night is a credible underlying mechanism that is supported by experimental and epidemiologic research. The proposed research will test the hypothesis that EMF and rotating shift work are risk factors for breast cancer among women textile workers in Shanghai. The textile industry is an especially suitable setting for investigating these associations because it entails some of the highest EMF exposures that occur occupationally or residentially. Furthermore, rotating shiftwork that uniformly included night (""""""""graveyard"""""""") shifts has been a widespread practice. This investigation will be a case-cohort study of 1414 incident breast cancer cases and a comparison group of 4219 noncase (""""""""controls""""""""), nested within a cohort of approximately 267,000 workers previously enumerated for an intervention trial of breast self exam, and currently being studied for associations of breast and other cancers in relation to occupational chemical and dust exposures. The principal research objectives of the proposed study are: 1) to quantify cases' and controls' EMF exposures, based on direct job-specific EMF measurements, historical documentation of equipment and other technological changes in the industry, and EMF measurements taken on vintage equipment; 2) to reconstruct subjects' past experience working rotating shifts; 3) to estimate dose-response relations for EMF and rotating shift work in relation to breast cancer risk. We will control for potential confounding by age, reproductive history, smoking, alcohol, diet, and other textile industry exposures (e.g., solvents) on the observed associations of breast cancer with EMF and rotating shiftwork. Particular advantages of this study are a large, clinically well characterized breast cancer case group, quantitative EMF assessment across a wide range of exposure levels, simultaneous investigation of rotating shift work, and detailed data on the most relevant potential confounders. Thus, this study should remedy many of the shortcomings of most previous epidemiologic research on EMF, shiflwork, and breast cancer, which has produced highly controversial findings. The results of our study should generate important new epidemiologic information that may suggest breast cancer prevention strategies in women textile workers and other women with similar exposures.
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