Breast cancer, lactation history, and serum organochlorines

The authors analyzed the relation between lactation history, organochlorine serum levels-in particular, 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE)-and the risk o f breast cancer within a subsample from a larger breast cancer case-control study conducted among women living in Mexico City, Mexico, between 1990 an d 1995. From the original study, they selected a random sample of 260 subje cts (1:1 case/control ratio). Analysis was restricted to 120 cases and 126 controls who had given birth to at least one child and had complete informa tion on all key variables. Serum DDE levels were higher among cases (mean = 3.84 mu g/g lipids, standard deviation = 5.98) than among controls (mean = 2.51 mu g/g lipids, standard deviation = 1.97). After adjustment for age, age at menarche, duration of lactation, Quetelet index, and serum DDT level s, serum DDE levels were positively related to the risk of breast cancer (a djusted odds ratio (OR)(Q1-Q2) = 1.24, 95% confidence interval (CI): 0.50, 3.06; ORQ1-Q3 = 2.31, 95% CI: 0.92, 5.86; ORQ1-Q4 = 3.81, 95% CI: 1.14, 12. 80; test of trend, p = 0.02). The increased risk associated with higher ser um DDE levels was more apparent among postmenopausal women (ORQ1-Q4 = 5.26, 95% CI: 0.80, 34.30; test of trend p = 0.03). A longer period of lactation was associated with a slightly decreased risk of breast cancer independent ly of serum DDE levels (OR = 0.91, 95% CI: 0.85, 0.99 change in risk per 10 months of lactation). Serum DDT level was not related to the risk of breas t cancer. The data suggest that high levels of exposure to DDE may increase women's risk of breast cancer, particularly among postmenopausal women.