Association between residence on Cape Cod, Massachusetts, and breast cancer.

Purpose: Massachusetts cancer registry and case-control data suggest that breast cancer incidence is elevated on Cape Cod relative to other parts of the state. We examined the association between length of residence on Cape Cod and breast cancer, since residential history could be acting as a surrogate for unidentified environmental risk factors.

Methods: We computed odds ratios (OR) and 95% confidence limits (CL) for 1121 cases occurring between 1988 and 1995 on Cape Cod and 992 controls, according to categories of residence time on Cape Cod, after adjusting for age, family history, parity and age at first live or stillbirth, education, body mass index, and breast cancer history.

Results: Breast cancer risk was elevated among women living on Cape Cod 5 or more years with a peak occurring in the 25 to less than 30 year category (adjusted OR=1.72; 95% CL, 1.12, 2.64). Adjusting for confounding strengthened the associations. Odds ratios did not increase monotonically over categories of longer residence.

Conclusions: Our results suggest that longer residence on Cape Cod is associated with elevated breast cancer risk, however inconsistency in the pattern of association limits conclusions that might be drawn about it. Suspected environmental exposures include pesticides and drinking water contaminated by industrial, agricultural, and residential land use.