Abstract A99: Passive smoking increases the risk of breast cancer among pre-and post-menopausal Mexican women
Authors: Chilian-Herrera Olivia L. , Cantor Kenneth P. , Hernández-Ramírez Raúl U. , López-Carrillo Lizbeth 
Published: December 2010

Background: Active and passive tobacco smoke exposures are considered modifiable risk factors for female breast cancer (BC). According to a recent expert panel report, active smoking (AS) increases the risk of BC by 20%, while the association between passive smoking (PS) and BC in younger, primarily premenopausal women who have never smoked, is consistent with causality; however, the evidence for risk among post menopausal women is inconclusive [Canadian Expert Report, 2009].

Since 2006, BC has become the leading cause of female cancer in Mexico, followed by cervical malignant tumors, with highest incidence in Mexican northern states [Knaul, 2009]. According to the National Surveys of Addictions, 6.5 million Mexican women between 12 and 65 years who have never smoked are currently exposed to environmental tobacco smoke. The mean age of tobacco smoking onset decreased from 18.3 years in 2008 to 16.8 years in 2009 [ENA, 2008; GATS, 2009].

Objective: To estimate the risk of breast cancer due to lifetime tobacco passive smoking exposure among pre and postmenopausal women residing in Mexico-US border states; to estimate risk associated with active smoking; and to explore age windows of susceptibility for both passive and active exposures.

Methods: The first 504 histologically confirmed incident BC cases and 504 age-matched controls from an ongoing population-based case-control study, are included in this analysis. Active (number of cigarettes/year) and passive (number of smokers/year) lifetime tobacco exposures, at home and the workplace, targeting periods of suspected susceptibility (i.e. puberty until first birth etc.) were estimated from direct interviews. Never active smokers without a history of passive smoking exposure were considered as the referent group and were compared with active smokers as well as passive smokers with no history of active smoking. Known reproductive BC risk factors were included as covariables in multivariate logistic regression models.

Results: Passive smoking significantly increased BC risk (OR t3 vs. t1 =3.34,95% CI 2.38-4.68, p for trend&lt;0.001) even after stratifying by menopausal status (OR premenopausal t3 vs. t1 =4.75,95% CI 2.58-7.35, p for trend&lt;0.001, OR postmenopausal t3 vs. t1 = 2.83,95% CI 1.87-4.28) and by age windows of susceptibility (i.e. 20 to 39 years OR t3 vs. t1 =2.68,95% CI 1.87-3.83, p for trend&lt;0.001). In the overall population, BC risk was also associated with active smoking (OR t3 vs. t1 =1.72,95%CI 1.11-2.69, p for trend&lt;0.001) that remained significant only when the age of tobacco smoking onset was between menarche and first birth (OR t3 vs. t1 =1.93,95%CI 1.19-3.23, p for trend&lt;0.001).

Conclusions: Our results provide evidence that PS is a risk factor not only for premenopausal but also for postmenopausal Mexican women and confirm that active smoking is a risk factor for this tumor.

Citation Information: Cancer Epidemiol Biomarkers Prev 2010;19(10 Suppl):A99.