Residential exposure to estrogen disrupting hazardous air pollutants and breast cancer risk: the California Teachers Study.

BACKGROUND: Some studies show increased breast cancer risk from exposure to xenoestrogens, but few have explored exposures via ambient air, which could impact large populations.

OBJECTIVES: This study explored the association between breast cancer risk and residential exposures to ambient estrogen disruptors among participants in a large cohort study, the California Teachers Study.

METHODS: Participants consisted of 112,379 women free of breast cancer and living at a California address in 1995/1996. Eleven hazardous air pollutants from the US Environmental Protection Agency 2002 list were identified as estrogen disruptors based on published endocrine disrupting chemical lists and literature review. Census-tract estrogen disruptor air concentrations modeled by the US Environmental Protection Agency in 2002 were assigned to participants' baseline addresses. Cox proportional hazards models were used to estimate hazard ratios associated with exposure to each estrogen disruptor and a summary measure of nine estrogenic hazardous air pollutants among all participants and selected subgroups, adjusting for age, race/birthplace, socioeconomic status, and known breast cancer risk factors.

RESULTS: Five thousand three hundred sixty-one invasive breast cancer cases were identified between 1995 and 2010. No associations were found between residential exposure to ambient estrogen disruptors and overall breast cancer risk or hormone receptor-positive breast cancer risk, nor among targeted subgroups of participants (pre-/peri-menopausal women, post-menopausal women, never-smokers, non-movers, and never-smoking non-movers). However, elevated risks for hormone receptor-negative tumors were observed for higher exposure to cadmium compounds and possibly inorganic arsenic among never-smoking non-movers.

CONCLUSION: Long-term, low-dose exposure to ambient cadmium compounds or possibly inorganic arsenic may be a risk factor for breast cancer.