GEO3N: environmental exposure to dioxins and breast cancer risk in the E3N cohort

In France, breast cancer is the leading cause of death in women. Its incidence has doubled over the last 30 years. In addition to an aging population and more widespread breast cancer screening, the hypothesis of environmental factors with endocrine-disrupting properties has been suggested to explain the rise in breast cancer incidence. These factors include dioxins, which are released during combustion processes of chlorinated organic materials. The French E3N national cohort (98 995 women who have been followed up since 1990) offers the opportunity to study the impact of environmental exposure to dioxins on breast cancer risk while taking the residential history of its members and their individual breast cancer risk factors into account. The objective of the GEO3N project was to study the association between environmental exposure to dietary and airborne dioxins and breast cancer risk. We assessed the association between estimated dietary dioxin exposure and breast cancer risk in 63 830 women from the E3N cohort (including 3 465 women with breast cancer). No statistically significant association was observed. The dioxin-emitting industrial sources in mainland France between 1990 and 2008 were identified (N=2620). The residential history of the E3N participants was geocoded, and 78% were located at the address level. A spatialized indicator for airborne dioxin exposure was developed by using a Geographic Information System (GIS) that took into account major dioxin dispersion parameters. Breast cancer risk associated with airborne dioxin exposure was estimated in 4529 case women with breast cancer matched to 4529 control women without it. In the Rhone-Alpes region (429 breast cancer cases matched to 716 controls), no statistically significant association was observed between airborne dioxin exposure and breast cancer risk. Analyses are still ongoing at the national level. Strong biological hypothesis and results from previous studies support the utility of further investigation into the effect of pollution exposure on breast cancer risk.