Why a Lactation-Stopping Drug Is Being Studied to Cut Breast Cancer Risk
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Image credit: Harbin · Public domain · Wikimedia Commons
In brief
A new study links cabergoline, a drug already used to stop breast milk production, to a lower chance of developing breast cancer after childbirth. Researchers who analyzed health records of more than 150,000 women in Spain and Norway, plus mouse experiments, say the drug speeds up a natural tissue-clearing process in the breast after weaning. Human clinical trials, not yet approved for cancer prevention use, are now being organized.
A study published in the journal Cancer Discovery on October 15, 2026, reports that cabergoline — a medication already prescribed to suppress milk production after childbirth — is associated with a sharply lower rate of breast cancer in the following years, according to the University of British Columbia (UBC), which co-led the research, and the Cancer Research Center at the Spanish National Research Council (CSIC) and the University of Salamanca, a partner institution.
What the researchers found
The team, led by UBC professor Christopher Maxwell and Jesús Pérez-Losada of the Cancer Research Center in Salamanca, analyzed health records from Spain and Norway covering more than 150,000 women, according to UBC News and News-Medical.net. Women who had taken cabergoline to suppress lactation were around 70% less likely to develop breast cancer in the years that followed, compared with women who had not taken the drug, both outlets reported.
In a separate laboratory arm of the study, researchers gave a single dose of cabergoline to mice carrying mutations in the BRCA1 and TP53 genes — mutations linked to aggressive, hereditary forms of breast cancer. Tumor incidence in these mice fell by roughly half, according to UBC and News-Medical.net.
The mechanism: finishing a natural process
The proposed explanation centers on a process called mammary gland involution. After a woman stops breastfeeding, milk-producing breast tissue that is no longer needed is normally broken down and cleared away by the body. According to UBC News, cabergoline appears to make this clearing process more complete — reducing precancerous tissue, shrinking the ductal area of the breast, slowing cell growth, and increasing the presence of immune cells that remove damaged cells.
Tribuna Salamanca, reporting on the same study, described the drug as helping the breast complete this post-weaning cleanup more thoroughly than happens on its own, reducing the window in which abnormal cells can persist.
But our findings suggest there may be an opportunity to reduce that risk with an existing drug by helping the breast complete a natural process that happens after breastfeeding ends.
— Christopher Maxwell, UBC professor and study co-lead, via UBC News
Who this could matter for — and what comes next
The researchers stress that cabergoline is not currently approved as a breast cancer prevention drug, and that findings from medical records and mice are not the same as proof from a controlled human trial. UBC News and News-Medical.net both report that human clinical trials are now needed to confirm the benefit and establish safe use.
A multinational clinical trial, funded by the Gray Foundation, is already being organized specifically for women carrying BRCA1 mutations, who face a substantially higher lifetime risk of breast cancer, according to UBC News. In the planned trial design, participants would choose how long to breastfeed, then receive either cabergoline or a placebo after weaning while researchers track biological markers linked to cancer risk.
News-Medical.net notes that existing prevention options for high-risk women, such as preventive hormone therapy or surgery, carry significant side effects, which is part of why researchers are interested in an intervention timed to the narrow post-weaning window rather than long-term medication.
Funding and study details
According to UBC News, the research was funded by the Canadian Institutes of Health Research, the Canadian Cancer Society, the Terry Fox Research Institute, Spain's Ministerio de Ciencia e Innovación, and additional agencies in the UK and US. News-Medical.net lists the study's lead authors as García-Sancha and colleagues, published in Cancer Discovery with the identifier DOI: 10.1158/2159-8290.CD-26-0187.
Key figures from the study
Measure
Finding
Source
Women in health-record analysis
More than 150,000 (Spain and Norway)
UBC News; News-Medical.net
Breast cancer risk reduction in cabergoline users
~70% lower, compared with non-users
UBC News; News-Medical.net
Tumor reduction in BRCA1/TP53-mutant mice
~50% lower incidence after single dose
UBC News; News-Medical.net
Current approval status for cancer prevention
Not approved; human trials needed
News-Medical.net
Questions
What is cabergoline normally used for?
Cabergoline is a medication already used to suppress milk production in women who stop breastfeeding, according to UBC News and News-Medical.net.
Does this mean cabergoline now prevents breast cancer?
No. The findings come from an analysis of medical records and from mouse experiments; researchers say human clinical trials are still needed before cabergoline could be used for cancer prevention, according to UBC News and News-Medical.net.
How much lower was breast cancer risk in women who used the drug?
Women who had taken cabergoline to suppress lactation were about 70% less likely to develop breast cancer in subsequent years than women who had not, based on health records of more than 150,000 women in Spain and Norway, according to UBC News and News-Medical.net.
Who is being recruited for the planned clinical trial?
A multinational trial funded by the Gray Foundation is being organized for women carrying BRCA1 gene mutations, who will choose how long to breastfeed and then receive cabergoline or a placebo after weaning, according to UBC News.
How does the drug supposedly lower cancer risk?
Researchers say cabergoline speeds up mammary gland involution, the natural process that clears milk-producing tissue after weaning, reducing precancerous tissue and increasing immune cells that remove damaged cells, according to UBC News.
How the world is telling it
SpanishTribuna Salamanca, covering the Salamanca-led side of the research, frames the story around the Cancer Research Center of Salamanca's role and describes the drug as helping the breast complete the post-weaning tissue cleanup more fully, noting that the planned clinical trial will initially target women with BRCA1 mutations.
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