Breast cancer and exposure to tobacco smoke during potential windows of susceptibility
Menée aux Etats-Unis à partir de données portant sur 50 884 participantes âgées entre 35 et 74 ans, cette étude prospective évalue l'association entre le tabagisme, actif et passif, et le risque de cancer du sein, en fonction du moment de l'exposition au tabac (1 843 cas ; durée moyenne de suivi : 6,4 ans)
Purpose : An association between smoking and breast cancer is unresolved, although a higher risk from exposure during windows of susceptibility has been proposed. The objective of this prospective study was to evaluate the association between tobacco smoke and breast cancer with a focus on timing of exposure, especially during early life. Methods : Sister study participants (n = 50,884) aged 35–74 were enrolled from 2003 to 2009. Women in the United States and Puerto Rico were eligible if they were breast cancer-free but had a sister with breast cancer. Participants completed questionnaires on smoking and environmental tobacco smoke (ETS) exposure. Cox regression was used to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (95% CIs) for breast cancer risk. Results : During follow-up (mean = 6.4 years), 1,843 invasive breast cancers were diagnosed. Neither active smoking nor adult ETS was associated with breast cancer risk. However, never smoking women exposed to ETS throughout their childhood had a 17% higher risk of breast cancer (95% CI 1.00–1.36) relative to those with no exposure. In utero ETS exposure was also associated with breast cancer (HR = 1.16, 95% CI 1.01–1.32) and the HR was most elevated for women born in earlier birth cohorts (<1940, HR = 1.44, 95% CI 1.02–2.02; 1940–1949, HR = 1.28, 95% CI 1.01–1.62). Conclusion : In utero ETS and ETS exposure during childhood and adolescence were associated with increased risk of breast cancer and associations varied by birth cohort.