Breastfeeding Support May Reduce TNBC Incidence, Mitigate Disparities

"Policy changes aimed at supporting and more broadly enabling breastfeeding, addressing structural barriers, and promoting a culture shift could reduce overall incidence and racial disparities in TNBC incidence in the [US]," according to the study authors.

Better support for breastfeeding may help avoid new cases of triple-negative breast cancer (TNBC) in patients who are White or Black, according to findings from a pooled analysis study published in NPJ Breast Cancer.1

Breastfeeding for less than 6 months conferred higher odds of TNBC for those who were White (pooled odds ratio [pOR], 1.41; 95% CI, 1.15-1.74; I2 = 67%) or Black (pOR, 1.35; 95% CI, 1.06-1.73; I2 = 0%). The pOR of developing TNBC after breastfeeding for less than 6 months was 1.16 (95% CI, 1.03-1.31; I2 = 74%) across all patients. The population-attributable fraction (PAF) of breastfeeding for less than 6 months was 12% (95% CI, 5%-20%) and 15% (95% CI, 3%-26%) in those who were White and Black, respectively.

Regarding all cases of TNBC diagnosed in 2022, 4850 could be attributed to breastfeeding for less than 6 months and/or being less than 25 years of age at time of first birth. Additionally, for 2421 individuals who were White and 1533 who were Black, annual TNBC cases were attributable to no breastfeeding or breastfeeding for less than 6 months and/or being younger than 25 at time of first birth. Investigators noted that 12% (n = 2421) and 15% (n = 861) of annual TNBC cases in patients who were White and Black, respectively, could specifically be attributed to a breastfeeding duration of less than 6 months.

“[W]e provide evidence supporting the benefits of breastfeeding not only for children but also for their mothers. We estimate that up to 15% of annual new TNBC in Black women and 12% in White women might be avoided by better supporting breastfeeding,” lead study author Rachel Jaber Chehayeb, a rising MS4 at the Yale School of Medicine, wrote with coauthors.1 “Policy changes aimed at supporting and more broadly enabling breastfeeding, addressing structural barriers, and promoting a culture shift could reduce overall incidence and racial disparities in TNBC incidence in the [US].”

According to the study authors, reproductive risk factors for developing TNBC include the lack of, or short duration of, breastfeeding and early pregnancy, with breastfeeding potentially limiting the risk of developing luminal or estrogen receptor–positive disease.2 Additionally, they described how the incidence of risk factors for TNBC has appeared to differ based on self-reported race in the US. With this background in mind, investigators assessed how differences in the prevalence of risk factors contribute to differences in TNBC incidence across Black and White populations by retrieving studies on breastfeeding and risk of TNBC.

Investigators conducted a PubMed search to identify articles from case-control and cohort studies based in the US that assessed the relationship between breastfeeding and TNBC risk. After an initial retrieval of 1326 items from PubMed, 15 articles were full text reviews. Of these items, 5 were ultimately included in the analysis.

Using pORs as an estimate for relative risk across these studies, investigators calculated the PAF, which quantifies the proportion of disease that is attributable to exposure to a specific risk factor in a certain population. Investigators also evaluated the PAF of age at first birth being less than 25 years and the combined effect of short or absent breastfeeding and early pregnancy on TNBC development.

Having a child before the age of 25 years represented a significantly higher risk of TNBC in those who were Black (pOR, 1.39; 95% CI, 1.08-1.78; I2 = 84%) but not those who were White (pOR, 1.06; 95% CI, 0.86-1.29; I2 = 84%). Additionally, the PAF for first birth at less than 25 years old ranged from 2% (95% CI, –6% to 11%) to 21% (95% CI, 5%-35%) for those who were White and Black, respectively.

Using race-specific pORs, the combined PAF for breastfeeding for less than 6 months and being younger than 25 years at time of first birth ranged from 8.6% to 26.7% for White and Black populations, respectively.

References

1. Chehayeb RJ, Odzer N, Albany RA, et al. Breastfeeding attributable fraction of triple negative breast cancer in the US. NPJ Breast Cancer. 2025;11(1):40. doi:10.1038/s41523-025-00755-6.
2. Lambertini M, Santoro L, Del Mastro L, et al. Reproductive behaviors and risk of developing breast cancer according to tumor subtype: a systematic review and meta-analysis of epidemiological studies. Cancer Treat Rev. 2016;49:65-76. doi:10.1016/j.ctrv.2016.07.006.