Drug already available on the NHS shows promise in preventing breast cancer in women before the menopause

Scientists at the Manchester Breast Centre, based at The University of Manchester, discovered a new purpose for the drug ulipristal acetate. They found that blocking the effects of the hormone progesterone using ulipristal acetate may reduce the risk of breast cancer developing.

The team hope their new research could provide women who have a strong family history of the disease with more options in the future.

Progesterone is a hormone that can drive breast cancer in some cells. It can switch on signals that help cells grow, multiply and survive and can also influence the environment inside the breast, making it easier for cancer cells to grow.

Blocking the effects of progesterone could be a new way to stop breast cancer before it starts. Ulipristal acetate is already used on the NHS, primarily as an emergency contraceptive and to treat non-cancerous growths that develop in or around the womb called uterine fibroids.

The researchers found that the drug helped block the growth of breast cells that can turn into cancer, called luminal progenitors. These cells are believed to be the starting point for triple negative breast cancer, an aggressive subtype of the disease more commonly found in younger women and black women.

Between 2016 and 2019, 24 women aged 34-44 took ulipristal acetate for 12 weeks. Before and after treatment, they had breast biopsies, blood tests and MRI scans so researchers could measure changes in their breast tissue.

Over the course of the 12-week treatment, MRI scans showed that breast tissue became less dense. And higher breast density is linked to an increased risk of breast cancer. 

Scientists also saw changes in the structure of breast tissue, including reduced levels of certain collagen proteins and softer tissue overall. This is important because when breast tissue is more stiff, it can create an environment that can help cancers develop and grow.

One collagen protein in particular, collagen 6, was noticeably decreased after treatment. And based on their findings, researchers now think that this protein may directly influence the behaviour of the luminal progenitor cells that can cause breast cancer. 

Together, these changes suggest that ulipristal acetate changes breast tissue in a way that makes it harder for cancer cells to develop and grow - reducing the risk of breast cancer.

The study focused on women before the menopause who had a strong family history of breast cancer. Currently, women at an increased risk of breast cancer have only 2 options to reduce their risk - surgery or long-term hormone therapy, both of which have a profound impact on physical and emotional wellbeing. 

Grace Burton, now aged 27 and living in Bromley, Greater London, was just 21 years old when she found out she carried a BRCA1 gene change. Suddenly, breast cancer had stopped being something that happened to other people. And in 2024, Grace made the difficult decision to undergo a preventative double mastectomy. 

For Grace, and many women like her, this study represents more than just scientific progress.

This early-stage study involved a small group of women over a short period of time, so larger and longer-term trials are now needed. But it provides promising evidence that targeting progesterone could one day offer women at higher risk a new way to prevent the development of breast cancer.

Research like this brings us closer to a future where fewer women must face the fear, uncertainty and difficult decisions that come with a high risk of breast cancer. And with your support, we’ll continue to fund research to make that future a reality.

This study was funded by Breast Cancer Now and supported by Prevent Breast Cancer. Several of the researchers were also supported by the National Institute for Health and Care Research (NIHR) Manchester Biomedical Research Centre (BRC). The research is published in Nature Journal.