Pre-diagnostic breastfeeding, adiposity, and mortality among parous Hispanic and non-Hispanic white women with invasive breast cancer: the Breast Cancer Health Disparities Study.

Background: U.S. Hispanic women have high rates of parity, breastfeeding, and obesity. It is unclear whether these reproductive factors are associated with breast cancer (BC) mortality. We examined the associations between breastfeeding, parity, adiposity and BC-specific and overall mortality in Hispanic and non-Hispanic white (NHW) BC cases.

Methods: The study population included 2921 parous women (1477 Hispanics, 1444 NHWs) from the Breast Cancer Health Disparities Study with invasive BC diagnosed between 1995 and 2004. Information on reproductive history and lifestyle factors was collected by in-person interview. Overall and stratified Cox proportional hazard regression models by ethnicity, parity, and body mass index (BMI) at age 30 years were used to calculate hazard ratios (HR) and 95% confidence intervals (CI).

Results: After a median follow-up time of 11.2 years, a total of 679 deaths occurred. Pre-diagnostic breastfeeding was associated with a 16% reduction in mortality (HR 0.84; 95% 0.72-0.99) irrespective of ethnicity. Parity significantly modified the association between breastfeeding duration and mortality (p interaction = 0.05), with longer breastfeeding duration associated with lower risk among women who had ≤2 births (p trend = 0.02). Breastfeeding duration was associated with reduced risk of both BC-specific and overall mortality among women with BMI <25 kg/m, while positive associations were observed among women with BMI ≥25 kg/m (p interactions <0.01).

Conclusion: Pre-diagnostic breastfeeding was inversely associated with risk of mortality after BC, particularly in women of low parity or normal BMI. These results provide another reason to encourage breastfeeding and weight management among young women.