A team of Japanese researchers said they have succeeded in separating and killing a subgroup of drug-tolerant breast cancer stem cells by using existing medicines currently used for heart failure.

The study, published Thursday in the Journal of Clinical Investigation, could lead to the future development of a therapy for patients with so-called triple-negative breast cancer (TNBC), said the team led by Noriko Goto at Kanazawa University.

The term “triple-negative” means the cancer cells don’t have estrogen or progesterone receptors and also don’t make the protein called HER2.

TNBC is known to grow faster than typical cancers, has fewer treatment options and tends to present a more negative outlook for patients.

Using cancer cells from breast cancer patients, the researchers performed single-cell RNA sequencing to analyze their genetic characteristics. This allowed the team to identify types of cancer stem cells that showed strong tolerance to drugs currently used in breast cancer treatment. Then they separated such cancer cells by identifying a protein called FXYD3, which was expressed on their cell membranes.

Furthermore, when researchers transplanted the cancer stem cells in mice and administered an existing heart failure drug known as cardiac glycosides as well as anti-cancer chemical agents, they found that the stem cells disappeared.

The study — which has yet to be performed on humans — suggests that adding heart failure drugs to preoperative chemotherapy may prevent the development of further tumors after breast cancer treatment.

“Following further preclinical trials, if the efficacy is proven by clinical trials, and if cardiac glycosides are added to standard preoperative systemic therapy, the prognosis of breast cancer patients may be significantly improved,” the scientists said.

Nearly 100,000 people in Japan develop breast cancer annually, and the number of people dying from the cancer is on the rise. The situation is particularly dire for people with triple-negative breast cancers, which are believed to account for 10% to 20% of all breast cancers.