Breastfeeding and subsequent risk of 24 types of maternal cancer: a cohort study of Chinese women

BACKGROUND: Existing epidemiological evidence on breastfeeding and cancer risks is inconsistent, and no studies have thoroughly examined the relationship between breastfeeding and each site-specific cancer in China. We aimed to investigate these associations among parous Chinese women. METHODS: A total of 157,454 participants aged 40-75 years from 2012 to 2021 were recruited. Cox proportional hazards model was applied to explore the association between breastfeeding behaviors and cancer risks by hazard ratios (HRs) and corresponding 95% confidence intervals (CIs). RESULTS: 5,542 incident cancer cases were identified with a median follow-up of 4.81 years. The history of breastfeeding was statistically significantly associated with lower risk of breast cancer in the multivariate-adjusted model (HR = 0.78, 95%CI: 0.65-0.94). In addition, the risk of gallbladder cancer increased with increasing months of total breastfeeding (P-trend = 0.039), with a 51% increase in risk for each additional 12 months of breastfeeding (HR = 1.51, 95%CI: 1.12-2.02). The risk of breast cancer decreased with increasing months of total breastfeeding (P-trend = 0.015), with a 15% reduction in risk for each additional 12 months of breastfeeding (HR = 0.85, 95%CI: 0.76-0.95). The subgroup analyses according to menopausal status shows significant separations for colon-rectum cancer, uterus cancer, oesophagus cancer, and larynx cancer (all P-interaction < 0.05). In addition, significant linear associations were suggested concerning gallbladder cancer (P-overall = 0.0302, P-nonlinear = 0.6558) and breast cancer (P-overall = 0.0175, P-nonlinear = 0.5544). CONCLUSIONS: This study provides further support for the role of breastfeeding behavior in overall cancer and its 24 site-specific cancers.