Mortality risk in former smokers with breast cancer: Pack-years vs. smoking status
Menée auprès de 2 953 participantes, cette étude canadienne analyse le risque de mortalité chez des anciennes fumeuses survivantes d'un cancer du sein et conclut à la nécessité, pour calculer et prédire le risque de mortalité, de choisir la durée d'exposition au tabagisme tout au long de la vie plutôt que le statut tabagique actuel
It is unclear why successful quitting at time of breast cancer diagnosis should remove risk from a significant lifetime of smoking. Studies concluding this may be biased by how smoking is measured in many epidemiological cohorts. In the late 1990s, a randomized trial of diet and breast cancer outcomes enrolled early-stage female breast cancer survivors diagnosed within the previous 4 years. Smoking history and key covariate measures were available at study entry for 2,953 participants. Participants were followed for an average of 7.3 years (96% response rate). There were 10.1% deaths (83% from breast cancer). At enrollment, 55.2% were never smokers, 41.2% former smokers and 4.6% current smokers. Using current smoking status in a Cox regression, there was no increased risk for former smokers for either all-cause mortality [hazard ratio (HR) = 1.11; 95% confidence interval (CI) = 0.87–1.41; p-value = 0.42) or breast cancer mortality. However, when we categorized on extensive lifetime exposure, former smokers with 20+ pack-years of smoking (25.8%) had a significantly higher risk of both all-cause (HR = 1.77; 95% CI = 1.17–2.48; p-value = 0.0007) and breast cancer-specific mortality (HR = 1.62; 95% CI = 1.11–2.37; p-value = 0.01). Lifetime smoking exposure, not current status, should be used to assess mortality risk among former smokers.