Passive smoking and breast cancer risk among non-smoking Chinese women

Our purpose was to evaluate whether passive exposure to cigarette smoke may be related to breast cancer risk. Data from the Shanghai Breast Cancer Study, a large population-based study of 1459 breast cancer cases and 1556 controls aged 25-64 years, were analyzed. Respective response rates were 91.1% and 90.3%. Passive smoking questions were added to all face-to-face interviews 7 months into the study. Women were asked about exposure to their husbands' smoke at home as well as exposure in the workplace. Analyses were restricted to the 1013 cases and 1117 controls with passive tobacco smoke exposure data who had never actively smoked. Over 60% of controls reported some exposure to a husband's smoke and over 40% reported exposure to passive smoke in the workplace. Overall, there was no apparent association between any passive smoke exposure or exposure to a husband's smoke and breast cancer risk. There was some evidence of an elevated breast cancer risk associated with passive smoking exposure of 5 hr or more per day in the workplace (OR = 1.6, 95% confidence interval 1.0-2.4; p for trend = 0.02). This association warrants further investigation.