Clinical trials to begin in Vancouver after study finds lactation drug could reduce breast cancer risk

A global study has found that a well-tolerated lactation drug could reduce the risk of breast cancer in mothers, an unexpected discovery that could save the lives of women with a high risk of developing the disease.

The team, co-led by UBC researchers, found that women who took cabergoline, a medication used to stop milk production after pregnancy loss or when breastfeeding is not possible, were about 70 per cent less likely to develop breast cancer than those who did not take the drug.

Given the significance of the findings, clinical trials will be conducted in Vancouver, Toronto, the U.K. and Spain. Scientists are working on the clinical protocol and hope to test the first patient sometime next year.

For the study, published last week in Cancer Discovery, researchers analyzed the health records of more than 150,000 women in Spain and Norway. Those who had the cabergoline treatment had a much a lower incidence of postpartum breast cancer.

The findings confirmed what scientists already knew about the drug in mice.

One of the study’s co-authors is Dr. Chris Maxwell, a professor in UBC’s faculty of medicine and investigator at B.C. Children’s Hospital Research Institute. Breast cancer is the leading cause of cancer-related death among younger women, he emphasised, and the majority of these cancers occur during the years after pregnancy.

“Younger adult females have almost twice as much cancer as younger adult males, and that’s principally due to breast cancer,” he said.

Researchers tested cabergoline in mice carrying BRCA1 and TP53 mutations, which are associated with aggressive forms of breast cancer.

They found that tumour incidence rates fell by about half.

Maxwell described the structure of the cells in the mammary gland as being like a fruit tree.

Similar to how a tree receives energy from the sun and nutrients from the soil for fruit production, the mammary glad receives cues that encourage it to form new branches, in preparation for milk production, he explained.

“With pregnancy, you get more growth, you get more branching, and then prior to birth, you have what’s called the lactogenic switch, which is basically the tree bears fruit, and these fruit are called the alveolar cells, and they’re the ones that make milk,” he said.

Then when the mother is done breastfeeding the milk-producing cells regress just like leaves fall off a tree, he said. Cabergoline induces that regression by blocking a hormone called prolactin.

According to the study, postpartum breast cancer often carries a poor prognosis and urgently requires chemotherapy, particularly for women at elevated risk.

“The period of transitioning from lactation to post pregnancy is a period that we can intervene,” said Maxwell.

“We can utilize the natural process that occurs there to clear out the mammary gland and prevent development of a postpartum period breast cancer.”

For the clinical trials, women with the BRCA1 mutation will be recruited through high-risk clinics. With the BRCA1 mutation, women have a 70 to 80 per cent chance of developing the disease, said Maxwell.

Women will choose how long they want to breastfeed, and researchers will follow these women after they finish breastfeeding, and give them either cabergoline or a placebo. They will also monitor biological markers linked to future breast cancer risk.

If the trials are successful, doctors could prescribe the drug, giving women an option to avoid current and more invasive preventive measures such as a double mastectomy.

Researcher believe that by targeting post-lactational involution with cabergoline, they could prevent postpartum breast cancer, and that the drug could be prescribed as a low-risk chemotherapy-prevention strategy.

The study was funded by the Canadian Institutes of Health Research, the Canadian Cancer Society, the Terry Fox Research Institute, and from agencies in Spain, the U.K. and the U.S.