Indoor Wood-Burning Stove and Fireplace Use and Breast Cancer in a Prospective Cohort Study

BACKGROUND: Indoor burning of fuel for heating or cooking releases carcinogens. Little is known about the impact of indoor air pollution from wood-burning stoves or fireplaces on breast cancer risk. OBJECTIVES: In a large prospective cohort study, we evaluated the risk of breast cancer in relation to indoor heating and cooking practices. METHODS: Sister Study participants ([Formula: see text]) were recruited from 2003–2009. Breast cancer–free women in the United States or Puerto Rico, 35–74 y old, with a sister with breast cancer were eligible. Participants completed questionnaires on indoor heating and cooking practices for both their enrollment and their longest adult residence. Cox regression was used to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (95% CIs) for the association between indoor heating/cooking and breast cancer. RESULTS: A total of 2,416 breast cancer cases were diagnosed during follow-up ([Formula: see text]). Having an indoor wood-burning stove/fireplace in the longest adult residence was associated with a higher breast cancer risk [[Formula: see text] (95% CI: 1.01, 1.22)]; the risk increased with average frequency of use [[Formula: see text] , [Formula: see text] (95% CI: 1.02, 1.34)] ([Formula: see text]). An elevated HR was seen for women burning wood [[Formula: see text] (95% CI: 0.98, 1.21)] or natural gas/propane [[Formula: see text] (95% CI: 1.00, 1.32)]. No association was observed for burning artificial fire-logs [[Formula: see text] (95% CI: 0.85, 1.12)] except among women from western states [[Formula: see text] (95% CI: 1.02, 1.81)]. CONCLUSIONS: In this prospective study, using an indoor wood-burning stove/fireplace in the longest adult residence at least once a week and burning either wood or natural gas/propane was associated with a modestly higher risk of breast cancer. https://doi.org/10.1289/EHP827