Tobacco smoke contains a number of human carcinogens, and metabolites of cigarette smoke have been found in the breast fluid of smokers. However, studies examining the association between tobacco smoke and breast cancer risk have yielded inconsistent results. Many studies have not been able to independently assess the contributions of the timing of exposure, age of diagnosis, or genetic susceptibilities to the overall risk of breast cancer. In addition, many of these studies did not consider passive smoking exposures, or exposure to secondhand smoke, among nonsmokers.
Peggy Reynolds, Ph.D., of the California Department of Health Services, and her colleagues examined breast cancer risk among 116,544 women in the California Teachers Study who had reported their smoking status on a survey given to them when they enrolled in the study.
Between 1996 and 2000, 2,005 of the women were diagnosed with invasive breast cancer. The incidence of breast cancer among current smokers was approximately 30% greater than that among women who had never smoked, irrespective of whether they were compared to women who had or had not been exposed to passive smoking. Analysis of subgroups of active smokers revealed increased breast cancer risks among women who started smoking before age 20, who began smoking at least 5 years before their first full-term pregnancy, and who had a longer duration of smoking or who smoked 20 or more cigarettes per day.
Current smoking was associated with increased breast cancer risk in women without a family history of breast cancer but not among women with a family history of the disease. There was no statistically significant increase in breast cancer risk among former smokers, and there was no evidence of an association between passive smoking exposure and breast cancer risk.
"Our results, which suggest that active smoking may be associated with an increased risk of breast cancer, argue for further research that can account for heterogeneity in individual susceptibility," the authors write. "Exposures to tobacco smoke, if causally related to breast cancer, could offer one of the few available modifiable avenues for preventing this disease."
Contact: Ken August, California Department of Health Services, 916-440-7660; firstname.lastname@example.org.
Reynolds P, Hurley S, Goldberg DE, Anton-Culver H, Bernstein L, Deapen D, et al. Active smoking, household passive smoking, and breast cancer: Evidence from the California Teachers Study. J Natl Cancer Inst 2003;96:29-37.
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