Pesticide exposure and risk of breast cancer: a nested case-control study of residentially stable women living on Long Island.

We conducted a nested case-control study of women in the New York State cohort who lived on Long Island. We estimated the historical environmental exposure to pesticides in 105 women diagnosed with breast cancer between 1980 and 1992 and 210 age and race-matched controls in this cohort of long-term residentially stable women who completed a short mailed questionnaire in 1980. Prior agricultural land use was assessed from aerial photographs taken in 1947 and 1950. Pesticides detected in drinking water were estimated from measures taken between 1977 and 1992. Geographic information system software was used to calculate the distance between residences and hazardous waste sites (HWS) containing pesticides. We found an increased breast cancer risk for women residing within 1 mile of HWS containing organochlorine pesticides (odds ratio [OR]=2.8; 95% confidence interval [CI], 1.1-7.1), after adjusting for other risk factors. A significant interaction was shown for women residing on land that was previously used for agriculture and women who were either nulliparous or had an older age at first birth (> or =26 yr old), compared to women who did not live on previously agricultural land and with a younger age (<26 yr old) at first birth (OR=6.4; 95%CI, 2.2-18.2). Study power was limited and confidence intervals were wide. Our findings suggest that exposure to pesticides in the environment needs to be more comprehensively investigated in relation to breast cancer risk.