Breastfeeding Associated with Reduced Mortality in Women with Breast Cancer

Objective: To study whether breastfeeding affects survival from breast cancer. Background: There are few studies on the relationship between breastfeeding, reproductive health, and breast cancer survival. This study is a follow-up of an earlier study showing no convincing associations between breastfeeding and breast cancer prognostic parameters. Methods: From a cohort of 629 women with primary breast cancer having undergone surgery between 1988 and 1992, 341 were traced and consequently studied 20 years later regarding breastfeeding and reproductive variables, as well as for prognostic parameters such as the Nottingham histological grade, tumor size, lymph node status, and vascular invasion (VI). Multivariate Cox regression analyses were used. Results: Increased breast cancer mortality was associated with the Nottingham prognostic index (hazard rate ratio (HR) 4.47; 95% confidence interval (CI) 2.04-9.79), VI (HR 3.44; CI 2.03-5.82), fewer pregnancies (three categories; >2, 1-2, 0) (HR per category 2.04; CI 1.34-3.11), and breastfeeding <= 6 months (HR 2.74; CI 1.41-5.35). The HRs for overall mortality were, as expected, lower for the Nottingham prognostic index (HR 1.28; CI 0.89-1.85) and VI (HR 2.09; CI 1.38-3.17), and they were slightly lower for the number of pregnancies (HR 1.61; CI 1.48-4.59), but notably similar for breastfeeding (HR 3.01; CI 1.92-4.73). Conclusion: A total breastfeeding history >6 months and pregnancy are associated with both greater overall and breast cancer-specific survival for women diagnosed with breast cancer, having lived long enough for other causes of death to contribute substantially to mortality.