A case-control interview study was used to evaluate the relationship between breast cancer risk and residential proximity to industrial facilities and traffic for pre-and postmenopausal women in Nassau and Suffolk Counties on Long Island, New York.

A geographic information system was used to assign industry and traffic counts to 1-km2 grid cells (5-km2 grid cells for traffic) and to assign potential exposure values to study subjects, based on 20-y residential histories.

A significantly elevated risk of breast cancer was observed among postmenopausal subjects who were ever potentially exposed to chemical facilities (Nassau County adjusted odds ratio [OR]=1.61,95% confidence interval [95% Cl]=1.06-2.43 ; Suffolk County adjusted OR=1.58,95% CI=0.71-3.51.

This elevated risk, however, was not observed among premenopausal subjects.

Risk increased for postmenopausal subjects as number of chemical facilities increased from one (adjusted OR=1.45,95% CI=0.93-2.25) to two or more (adjusted OR=3.47,95% CI=1.06-11.38).

Crude and adjusted ORs for high traffic density were elevated among Nassau-but not Suffolk-county subjects and were not significant statistically.