Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer that lacks expression of estrogen and progesterone receptors or the HER2 gene. Black women experienced a 19-28% TNBC, compared to a 9-14% risk among White women. Additionally, premenopausal women are more frequently diagnosed with this cancer. Some researchers attribute differences in breast cancer rates to genetic ancestry, but modifiable reproductive behaviors, including breastfeeding and first birth timing, also show an impact.
Researchers examine the role that reproductive risk factors play in determining the incidence of TNBC among Black and White American women. The research team used PubMed’s systematic review methods to find U.S. cohort and case-control studies that investigated the link between breastfeeding and TNBC. The year 2008 was chosen as the publication year cutoff, as HER2 testing was not widely implemented before then, which limited the ability to accurately classify TNBC cases. The analysis included complete reviews of 15 articles from 1,326 initial identifications and final data from 5 eligible case-control studies. Secondary analysis included an assessment of the age at first birth risk factor using data from the included studies.
The analysis used pooled odds ratios (pORs) as an estimate of the risk of TNBC development among women with brief breastfeeding duration (<6 months) and early first childbirth (<25 years). Population attributable fractions (PAFs) based on pORs calculated the proportions of these risk factors in producing TNBC cases attributable to these risk factors in Black and White women. Women who breastfed their babies for less than six months showed statistically higher TNBC risk in both racial groups.
Delivery at a young age, i.e., before age 25, was associated with a significantly higher risk of triple-negative breast cancer (TNBC) among Black women (pooled odds ratio [pOR] = 1.39, 95% CI: 1.08-1.78), but not among White women (pOR = 1.06, 95% CI: 0.86–1.29), with both cohorts having significant heterogeneity (I² = 84%). When a common-effects model was used, the overall pOR was 1.19 (95% CI: 1.01–1.39) after excluding the John et al. study. When the study was included, the pooled odds ratio was 1.19 (95% CI: 1.01-1.39), and 1.14 (95% CI: 1.01-1.29) when it was included, with I² values of 81% and 76%, respectively.
Among all women, the population attributable fraction (PAF) for having a first birth before age 25 was estimated at 7% (95% CI: 1-13%), increased to 9% (95% CI: 1-17%) when the study by John et al. was excluded. When analyzed by race, the PAF varied, ranging from 2% (95% CI: -6-11%) in White women to as high as 21% (95% CI: 5-35%) in Black women.
A study determined that 4,850 new TNBC cases in the U.S. for 2022 would result from these two risk factors affecting 2,421 White women and 1,533 Black women. A total of 2,421 White women and 861 Black women developed TNBC due to short breastfeeding durations, measuring at under six months. Research findings demonstrate the substantial impact that breastfeeding periods longer than six months, along with delayed first childbirth age, have on the development of TNBC.
An estimated 15% of annual TNBC cases in Black women and 12% in White women could be prevented with improved breastfeeding support. Public health requires specific intervention strategies like bolstered maternity care programs and workplace breastfeeding support combined with educational maternal health campaigns to display breastfeeding’s advantages. Public health interventions should address TNBC incidence while working to minimize racial disparities within this dangerous cancer subtype.
References: Chehayeb RJ, Odzer N, Albany RA, et al. Breastfeeding attributable fraction of triple negative breast cancer in the US. NPJ Breast Cancer. 2025;11:40. Breastfeeding attributable fraction of triple negative breast cancer in the US | npj Breast Cancer
