Results of a study of breast tissue from healthy parous women showed histologic and molecular differences depending on duration of breastfeeding. The findings of this study were presented at the 2019 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago, Illinois.

Epidemiological studies have demonstrated an association between the lack of breastfeeding in multiparous women and an increased risk of triple-negative breast cancer.2,3 These studies have shown a higher risk of triple-negative breast cancer in African-American women compared with Caucasian women of European descent, as well as a lower likelihood of breastfeeding in the former group.

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Interestingly, other studies of black women in South African countries, who have been reported to typically breastfeed their children for more prolonged periods, have shown a low incidence of hormone receptor-negative breast cancer in that population.4 Furthermore, previous studies performed in mice have identified differences in the morphology and molecular characteristics of mammary tissue depending on the duration of breastfeeding.

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In this study, the Susan G. Komen for the Cure Tissue Bank was mined for formalin-fixed paraffin-embedded breast tissue sections from healthy, premenopausal, parous women aged 18 to 45 years without a history of breast cancer, along with corresponding demographic and clinical characteristics including age at menarche, parity, age at first and last birth, and duration of breastfeeding.

Pathologic testing included an analysis of breast morphology, including the number and density of terminal ductal lobule units, degree of lobular differentiation, proliferation index (ie, as measured using Ki67 immunostaining), periductal collagen deposits, and gene-expression profiling (with a focus on genes involved in stem-cell and cell-renewal pathways).

A central finding of this study was that the breast tissue from women who breastfed for a total of fewer than 4 months (ie, termed abrupt involution) was distinctly different from the breast tissue of women with a cumulative breastfeeding period of 6 months or longer (ie, termed gradual involution).

 Specifically, a morphological analysis of 18 specimens and 48 specimens of breast tissue from women with shorter and longer breastfeeding durations, respectively, showed inflammatory features in the former group.

In addition, increased proliferation, less lobular differentiation, and an enrichment in stem-cell and cell-renewal pathways (ie, Notch and Sonic Hedgehog pathways) were observed in the breast tissue of those who breastfed for less than 4 months compared with breast tissue from women who breastfed for 6 months or longer. No difference in periductal collagen deposition was detected in breast tissue based on breastfeeding duration.

The study authors commented that these results “warrant a further investigation with a larger sample size.”

In their concluding remarks, the study authors noted that “experiments are underway to assess the long-term effect of breastfeeding on breast epithelial cell hierarchy and biomarkers of inflammation. Understanding this mechanistic link will help in developing prevention strategies, particularly for African-American women who have lower prevalence of breastfeeding and higher incidence of triple negative, basal-like breast cancers.”


  1. Basree M, Shinde N, Li Z, et al.  Analysis of healthy breast tissue from Komen Tissue Bank shows distinct histology, decreased proliferation, and lower periductal collagen deposition in women with prolonged history of breastfeeding. Presented at: 2019 American Society of Clinical Oncology (ASCO) Annual Meeting; May 31-June 4, 2019: Chicago, IL. Abstract 1538.
  2. Palmer JRViscidi ETroester MA, et al. Parity, lactation, and breast cancer subtypes in African American women: results from the AMBER Consortium. J Natl Cancer Inst. 2014;106(10):dju237.
  3. Ambrosone CB, Zirpoli G, Ruszczyk M, et al. Parity and breastfeeding among African-American women: differential effects on breast cancer risk by estrogen receptor status in the Women’s Circle of Health Study. Cancer Causes Control. 2014;25(2):259-265.
  4. Dickens CDuarte RZietsman A, et al. Racial comparison of receptor-defined breast cancer in Southern African women: subtype prevalence and age-incidence analysis of nationwide cancer registry data. Cancer Epidemiol Biomarkers Prev. 2014;23:2311-2321.