Background: Evidence shows that exposure to passive smoking increases the risk of breast cancer. However, there is a lack of data on the role of serum cotinine level among passive smoker women with breast cancer. The purpose of this study was to investigate the association of serum cotinine level and passive smoking exposure with the risk of breast cancer.
Method: We conducted this case-control study on 78 women with newly diagnosed breast cancer and 83 healthy women, aged 21 to 59 years. Neither cases nor controls were ever smokers in their lifetime. The serum cotinine level, as a biological marker of secondhand smoking, was assessed among women exposed to passive smoking.
Results: The mean serum cotinine concentrations were higher among cases compared to controls although the difference was not statistically significant (4.6 ± 3.5 ng/mL vs. 2.8 ± 2.2 ng/mL, respectively, P = 0.059). However, serum cotinine significantly increased the risk of breast cancer (OR = 1.22; 95% CI = 1.02, 1.48, P = 0.034). Exposure to passive smoking at home and exposure from a smoker husband increased the risk of breast cancer compared with those with no exposure (OR = 2.17; 95% CI = 1.15, 4.08, P = 0.016; and OR = 2.67; 95% CI = 1.35, 5.29, P = 0.005, respectively).
Conclusion: Serum cotinine levels and passive smoking exposure appeared to be independent risk factors associated with the development of breast cancer.