The importance of addressing early life environmental exposures in cancer epidemiology.

Purpose of Review: Environmental exposures during early stages of life may be particularly relevant for cancer etiology because of the rapid hormonal and tissue changes that occur during puberty and, in women, through first birth. We review evidence from the past five years on environmental exposures during childhood/adolescence through first birth and the risk of breast and other cancers during adulthood. Recent Findings: The studies of breast cancer (n=14) reported associations for childhood/adolescent environmental tobacco smoke (ETS), smoking initiation, pesticides, hair dye use, and living on a road with high traffic. Smoking before first childbirth was also associated with increased breast cancer risk. We identified 12 studies on other cancers, with only 1-2 studies per cancer type, with most focused on ETS or active smoking. Summary: Despite studies suggesting an important role of exposure to environmental factors during early life and cancer risk in adulthood, few studies have been conducted. Future studies could utilize stored biologic samples from relevant periods or complete residential histories for geographically-based exposures.