Breast cancer is the most common malignancy among Israeli Arab women who have low rates of active smoking (7%) and high rates of passive smoking due to the smoking prevalence in Arab men (44%). The role of smoking in breast cancer etiology is controversial. The enzyme N-Acetyl-Transferase 2 (NAT2) acetylates tobacco carcinogens and certain NAT2 genotypes (rapid/intermediate/ slow) may modify cancer risk.
To evaluate the relationship between passive smoking and breast cancer risk by NAT2 status in non-smoking Israeli Arab women.
A case-control study consisting of 137 prevalent breast cancer patients and 274 population-based controls. Each participant was face-to-face interviewed using a detailed questionnaire tracing demographic, lifestyle and other characteristics as well as exposure to passive smoking in childhood (age 0-12), adolescence (age 13-18) and the present, and donated a tissue sample for genetic testing.
The exposure to passive smoking was compared between cases and controls adjusting for known risk factors by logistic regression models. Modification of breast cancer risk by NAT2 status was also assessed.
Compared to the controls, cases were significantly older, had lower education and socioeconomic status, had later menopause and were more exposed to passive smoking in childhood, adolescence and the present. There were no differences in the NAT2 variants, with two thirds of both cases and controls having a slow acetylating phenotype. Following adjustment for potential confounders, the exposure to passive smoking was associated with increased risk for breast cancer, with an OR=2.1495%) CI 1.21-3.78). Additionally, longer exposure was associated with higher risk. NAT2 status did not modify these results.
Non-smokers highly exposed to passive smoking are at a higher risk for breast cancer, with a dose-response relationship. These results further stress the importance of smoking cessation for both the smokers and those exposed to it passively.