title: Active cigarette smoking and risk of breast cancer.
abstract: Although epidemiological evidence on the role of active cigarette smoking in breast cancer risk has been inconsistent, recent literature supports a modest association between smoking and breast cancer. This association is particularly observed in women who smoke for a long duration, or who smoke for a long time prior to their first pregnancy. Here, we provide updated results on cigarette smoking and breast cancer risk in the Canadian National Breast Screening Study (NBSS). The NBSS is a large cohort of 89,835 women, aged 40-59, who were followed for a mean of 22.1 years, resulting in the ascertainment of 6,549 incident cases of breast cancer. Cox proportional hazard models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the association of cigarette smoking variables with breast cancer risk. We found breast cancer to be associated with duration (40 years vs. 0: HR = 1.57; 95%CI = 1.29-1.92), intensity (40 cigarettes per day vs. 0: HR = 1.21; 95%CI = 1.04-1.40), cumulative exposure (40 pack-years vs. 0: HR = 1.19; 95%CI = 1.06-1.13) and latency (40 years since initiation vs. 0: HR = 1.19; 95%CI = 1.10-1.53) of cigarette smoking. Number of years smoked prior to first full-term pregnancy was associated with higher risk of breast cancer than comparative years smoked post-pregnancy (among parous women, 5 years pre pregnancy vs. 0: HR = 1.18; 95%CI = 1.10-1.26). These results strongly support a role for cigarette smoking in breast cancer etiology and emphasize the importance of timing of this exposure.
authors.affiliation: Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, New York, NY.
authors.forename: Chelsea
authors.initials: C
authors.lastname: Catsburg
authors.forename: Anthony B
authors.initials: AB
authors.lastname: Miller
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Rohan
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D002170:Canada / Q000453:epidemiology; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D011247:Pregnancy; D016016:Proportional Hazards Models; D012306:Risk; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D013997:Time Factors
keywords: breast cancer; cohort; smoking