Correlation of body mass index with serum DDTs predicts lower risk of breast cancer before the age of 50: prospective evidence in the Child Health and Development Studies

Many suspected breast cancer risk factors, including the pesticide dichlorodiphenyltrichloroethane (DDT) and its metabolite dichlorodiphenyldichloroethylene (DDE), are stored in fat where they could influence carcinogenesis. We tested the hypothesis that the relationship of DDT and DDE (DDTs) with adiposity is modified by disposition to develop breast cancer. We predicted that concentrations of serum DDTs would be inversely correlated with body mass index (BMI) during active exposure when DDTs move into the larger fat pool. We described this correlation at an average of 17 years before breast cancer was diagnosed, in a prospective nested case-control study in the Child Health and Development Studies. Women entered the study during pregnancy from 1959 to 1966 when DDT was in active use. In total, 133 breast cancer cases were diagnosed under the age of 50 as of 1998. Mean time to diagnosis was 17 years. In total, 133 controls were matched to cases on birth year. We observed the expected inverse correlation of serum DDTs with BMI only in women who remained cancer-free and not in women who ultimately developed breast cancer (p for interaction < 0.05). Findings suggest that vulnerability to breast cancer before the age of 50 may be associated with an uncoupling of the inverse correlation between BMI and serum DDTs. Investigation into mechanisms may eventually reveal early biomarkers of breast cancer risk.