Shift work and working at night in relation to breast cancer incidence
Menée aux Etats-Unis à partir de données de la cohorte "Sister study" portant sur 48 451 femmes (durée moyenne de suivi : 9,1 ans), cette étude analyse l'association entre les horaires de travail posté et le risque de cancer du sein (3 191 cas)
Background: Night shift work has been classified by the International Agency for Research on Cancer (IARC) as a probable carcinogen in humans. Several studies have assessed night shift work in relation to breast cancer risk, with inconsistent results. Methods: In the prospective Sister Study cohort, current and past occupational history was collected for 48,451 participants. We used Cox proportional hazards models to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between baseline work schedule characteristics and incident breast cancer. Results: During follow-up (mean=9.1 years), 3,191 incident cases were diagnosed. We observed little to no increase in risk associated with work schedule characteristics (ever working rotating shifts: HR=1.04, 95% CI: 0.91-1.20; ever working rotating night shifts: HR=1.08, 95% CI: 0.92-1.27; ever working at night: HR=1.01, 95% CI: 0.94-1.10; ever working irregular hours: HR=0.98, 95% CI: 0.91-1.06). While short-term night work (>0 to 5 years vs. never, HR=1.12, 95% CI: 1.00-1.26) or rotating shift work at night (>0 to 5 years vs. never, HR=1.30, 95% CI: 1.05-1.61) were associated with increased breast cancer risk, working nights for more than 5 years was not associated with risk. Conclusions: Overall, we observed little evidence that rotating shift work or work at night was associated with a higher risk of breast cancer, except possibly among those who participated in such work for short durations of time. Impact: This study indicates that if night shift work is associated with breast cancer, the increase in risk is small.