Research published in Nature on October 20, 2025, reveals that breastfeeding induces long-lasting immune protection in women by increasing specialized immune cells called CD8+ T-cells in the breast tissue, which can help protect against breast cancer.

Data from over a thousand breast cancer specimens show that tumors in women who have given birth have higher T cell infiltration and better outcomes, especially in triple-negative breast cancer (TNBC), suggesting reproductive history could inform personalized treatment strategies.

Mouse studies confirmed that parous mice who breastfed exhibited reduced tumor growth and increased T cell presence within tumors, with depletion of these T cells nullifying the protective effect, highlighting their role in cancer defense.

The research underscores the importance of supporting breastfeeding, as low exclusive breastfeeding rates in Australia (only 16% at six months) limit potential health benefits, calling for improved community and workplace support for mothers.

The study was published in Nature on October 20, 2025, by a large team of scientists from Australian institutions and international collaborators.

While recognizing that not all women can or want to breastfeed, researchers emphasize understanding the biological pathways involved to develop interventions that could provide similar immune protection for women unable to breastfeed.

Longer breastfeeding durations may enhance immunity, possibly through prolonged microbial exposure via the infant’s saliva, though determining the optimal length remains challenging due to reliance on observational data.

The involution phase after breastfeeding plays a crucial role in shaping immune memory by creating an environment rich in inflammatory signals that promote T_RM cell recruitment and retention, challenging the view of involution as merely a transient vulnerability.

Professor Loi highlighted that the protective effect of breastfeeding is cumulative, with more children breastfed correlating with a lower breast cancer risk, although societal factors influence breastfeeding practices.

Historical observations of nuns, who rarely gave birth, showed higher breast cancer rates, leading scientists to suspect reproductive factors influence breast cancer risk.

Future research should explore the molecular cues guiding T_RM cell differentiation and maintenance in the mammary gland, as well as how hormonal and inflammatory signals during reproductive events shape immune responses.

Women who have children but do not breastfeed, particularly African American women, face a higher risk of triple-negative breast cancer, emphasizing the importance of breastfeeding for risk reduction.