Establishing a link between cigarette smoking and breast cancer has so far proven to be difficult, and studies have been inconsistent in terms of whether smoking increases risk for the disease.
However, in a recent study from the Canadian National Breast Cancer Study, published in the International Journal of Cancer, has found a modest association between smoking and breast cancer risk in women, particularly in regards to duration of smoking. The data were based on a large cohort of women (89,835) between the ages of 40 and 59 years who were followed for 22 years. Of this group, 6,549 women were diagnosed with breast cancer.
The researchers used Cox proportional hazard models to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the association of cigarette smoking variables with breast cancer risk, including duration of smoking, intensity (ie, how many cigarettes were smoked per day), cumulative exposure, and amount of time since initiation of smoking.
Based on these variables, they concluded that the results strongly support a role for cigarette smoking in breast cancer etiology, particularly as it relates to when first exposure to smoking occurred, as a higher risk was seen in those women that smoked for a longer duration before their first pregnancy.
The authors provide updated results on cigarette smoking and breast cancer risk in the Canadian National Breast Screening Study (NBSS). The results strongly support a role for cigarette smoking in breast cancer etiology and emphasize the importance of timing of this exposure.