A recent study from the University of Cambridge has produced a detailed genetic atlas of the adult mammary gland, shedding light on genes involved in breastfeeding and providing new information about genetic links to breastfeeding disorders and postpartum breast cancers.
Researchers conducted their study in mice, analyzing how the mammary gland changes at ten different stages: before pregnancy, during pregnancy, throughout breastfeeding, and during involution—the process when breast tissue returns to its resting state after breastfeeding ends. This allowed them to identify which genes are active in various cell types at each stage.
“Our atlas is the most detailed to date, allowing us to see which genes are expressed in which cell types at each stage of the adult mammary gland cycle,” said Dr Geula Hanin, a researcher in the University of Cambridge’s Department of Genetics and first author of the report.
The findings revealed that genes linked to breastfeeding difficulties such as insufficient milk supply are not only active in milk-producing cells but also in basal cells. Basal cells help expel milk as an infant suckles. The researchers suggest this means some breastfeeding problems could be due to mechanical issues rather than solely production problems.
Additionally, the team discovered that genes associated with postpartum breast cancer become active immediately after weaning across multiple cell types—including fat cells, which have not been previously considered significant contributors to breast cancer related to childbirth. This insight could guide future strategies for early detection or prevention.
Hanin explained: “We’ve found that genes associated with problems in milk production, often experienced by breastfeeding mothers, are acting in breast cells that weren’t previously considered relevant for milk production. We’ve found genes associated with postpartum breast cancer acting in cells that have been similarly overlooked.
“This work provides many potential new ways of transforming maternal and infant health, by using genetic information to both predict problems with breastfeeding and breast cancer, and to tackle them further down the line.”
Breastfeeding is known to influence long-term health outcomes; for example, babies who are breastfed have lower risks of obesity and diabetes later in life. However, one in twenty women experience difficulties with breastfeeding. Despite its importance for health, this area remains under-researched.
Postpartum breast cancer typically develops within five to ten years after childbirth. It is linked with hormonal shifts and natural remodeling processes in the mammary gland during involution—a period that increases susceptibility to malignancy.
The study also focused on imprinted genes—genes whose activity depends on whether they come from the mother or father. The researchers identified 25 such genes active at specific times during mammary gland development. These imprinted genes appear important for regulating milk production and tissue changes during motherhood.
Some roles of these genes had been suggested by previous research; this new study adds detail about when and where these genetic changes happen during adult mammary gland development.
“Breastfeeding is a fundamental process that’s common to all mammals; we wouldn’t have survived without it. I hope this work will lead to new ways to support mothers who have issues with breastfeeding, so they have a better chance of succeeding,” said Hanin.
The Medical Research Council primarily funded this research. Hanin co-leads the Cambridge Lactation Network and is part of Cambridge Reproduction.
Reference: Hanin, G. et al: ‘Dynamic Allelic Expression in Mouse Mammary Gland Across the Adult Developmental Cycle.’ Nucleic Acids Research, September 2025. DOI: 10.1093/nar/gkaf804