Objective: This study focused on geographic clustering of breast cancer based on residence in early life and identified spatio-temporal clustering of cases and controls.
Methods: Data were drawn from the WEB study (Western New York Exposures and Breast Cancer Study), a population-based case-control study of incident, pathologically confirmed breast cancer (1996-2001) in Erie and Niagara counties. Controls were frequency-matched to cases on age, race, and county of residence. All cases and controls used in the study provided lifetime residential histories. The k-function difference between cases and controls was used to identify spatial clustering patterns of residence in early life.
Results: We found that the evidence for clustered residences at birth and at menarche was stronger than that for first birth or other time periods in adult life. Residences for pre-menopausal cases were more clustered than for controls at the time of birth and menarche. We also identified the size and geographic location of birth and menarche clusters in the study area, and found increased breast cancer risk for pre-menopausal women whose residence was within the cluster compared to those living elsewhere at the time of birth.
Conclusion: This study provides evidence that early environmental exposures may be related to breast cancer risk, especially for pre-menopausal women.