Abortion drug shows promise in reducing cancer risk

Mifepristone, widely used in medical abortions, may also lower breast cancer risk in women more likely to develop the disease.

Doctors and scientists say stigma surrounding mifepristone is deterring pharmaceutical firms from examining its use as a preventive drug, even though three studies suggest it can slow cancer cell growth.

They argue the drug’s link with abortion, along with restrictions in some countries, is blocking research that could have major public health benefits.

Mifepristone is one of two drugs, along with misoprostol, that women in the UK can use to end pregnancies up to 10 weeks.

Women take a mifepristone tablet, wait 24–48 hours and then take misoprostol. It works as a selective progesterone receptor modulator, meaning it blocks progesterone – a hormone known to drive cell growth in breast cancer.

“It is deeply disappointing that the successful application of mifepristone in one area of clinical medicine is hindering more extensive research into other indications that could benefit public health,” the eight co-authors wrote in The Lancet Obstetrics, Gynaecology and Women’s Health.

“The time is long overdue to give mifepristone the opportunity it deserves to be investigated as a non-surgical option for primary prevention.”

The authors, specialists in reproductive health and cancer, are based in London, Edinburgh, Stockholm and Erbil, Iraq.

Breast cancer kills about 670,000 women worldwide each year, according to the World Health Organization.

Mifepristone could prove particularly useful for women with BRCA1 or BRCA2 gene variants, who currently face limited choices beyond mastectomy or what the authors describe as “low efficacy” drugs.

Three small studies carried out in 2008, 2022 and 2024 showed the drug reduced progesterone’s effect on breast tissue cell growth.

UK cancer charities have joined calls for further research.

Dr Simon Vincent, chief scientific officer at Breast Cancer Now, said: “More risk-reducing treatment options for women with a high risk of developing breast cancer, that also protects their quality of life, are desperately needed. And we need to explore all avenues, including existing drugs, to achieve this.

“So early research into mifepristone is an important step forward and we need further studies to understand if these drugs are safe and effective.”

Dr Marianne Baker, Cancer Research UK’s science engagement manager, pointed to the UK’s 57,900 annual breast cancer cases as evidence that “it’s vital we invest in research exploring new ways to prevent the disease”.

She added: “Cancer develops when cells grow uncontrollably. Early studies showed that mifepristone slowed down cell growth in breast tissue, so it might be useful in delaying or preventing cancer.

“But we need more research to understand whether it’s effective, how it works and who would benefit most from it.”

Prof Kristina Gemzell Danielsson, the lead author and head of the department of women’s and children’s health at the Karolinska Institute in Stockholm, said: “Stigma around mifepristone used for abortion is describing part of why mifepristone is not more extensively researched for prevention of breast cancer.

“Taken together, our data support the use of mifepristone for prevention of poor prognosis breast cancer. All studies were randomised controlled trials using a low dose of mifepristone for two or three months.”