Active cigarette smoking and risk of breast cancer
Menée sur une cohorte canadienne de 89 835 femmes âgées de 40 à 59 ans (durée moyenne de suivi : 22,1 ans), cette étude évalue l'association entre différents paramètres du tabagisme (nombre de cigarettes consommées par jour, durée du tabagisme, ...) et le risque de cancer du sein (6 549 cas)
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.