Breast cancer, carcinogens and endocrine disruptors: A Canadian occupational study and strategy for future investigation

Background and Objectives: Endocrine disrupting chemicals and carcinogens in occupational environments may cause observable, excess breast cancer. This study examined breast cancer risk and occupation particularly in farming and manufacturing in SW Ontario. Methods: Detailed occupational, reproductive and demographic histories were obtained from 1006 cases and 1146 controls. Jobs were industry- and occupation-coded, exposure metrics constructed for likely exposure to carcinogens and endocrine disruptors, and data analyzed in a frequency-matched case-control design. Results: All women in jobs with potentially high exposures had elevated breast cancer risk (OR = 1.42 (95% CI, 1.18-1.73), for 10 years exposure duration). Specific sectors with elevated risk included: agriculture (OR = 1.36; 95% CI, 1.01-1.82); bars-gambling (OR = 2.28; 95% CI, 0.94-5.53); automotive plastics (OR = 2.68; 95% CI, 1.47-4.88), and metalworking (OR = 1.73; 95% CI, 1.02-2.92). Risk varied with tumor estrogen receptor status and was highest for premenopausal women in automotive plastics (OR = 4.76; 95% CI, 1.58-14.4) and food canning (OR = 5.70; 95% CI, 1.03-31.5). Conclusions: These observations support hypotheses linking breast cancer risk and exposures to carcinogens and endocrine disruptors. The value of occupational studies in breast cancer is affirmed. Based on these results priority objectives for investigation include: rigorous retrospective exposure assessments in automotive plastics and canning operations, confirmatory studies in similar populations, and identification of other populations potentially at high risk. Implications in the current breast cancer epidemic and the appropriate responses for the cancer research establishment will be discussed.