This 100-year-old treatment could revolutionize the fight against breast cancer.

A heart medication that’s been around for over 100 years, derived from the foxglove plant, might hold the key to fighting cancer. Swiss researchers have discovered that digoxin can break up clusters of circulating cancer cells, potentially stopping them from spreading throughout the body. This unexpected finding could pave the way for new treatments targeting metastasis, the leading cause of breast cancer deaths.

Breast cancer remains one of the leading causes of death among women in the U.S., largely due to its ability to spread to other organs. Most current treatments focus on destroying tumor cells but don’t directly address how cancer spreads. However, a study published in Nature Medicine in February 2025 suggests that a century-old heart medication could offer a complementary approach to preventing the spread of cancer cells.

How digoxin targets metastasis

Digoxin, a drug derived from Digitalis lanata (foxglove) in 1930, has long been used to treat heart failure and atrial fibrillation. It works by blocking sodium-potassium pumps in heart cells, leading to stronger contractions and a slower heart rate.

Now, scientists believe this same mechanism could be applied to cancer treatment. By inhibiting these pumps in tumor cells, digoxin increases calcium absorption. Previous studies have shown that elevated calcium levels disrupt key cell adhesion structures, weakening the tumor cells’ ability to stick together.

Circulating tumor cells play a crucial role in metastasis. When they clump together, they’re more likely to form new tumors in other parts of the body. By weakening the bonds between these cells, digoxin helps break up the clusters, potentially preventing them from spreading to other organs.

Early results are promising

Following successful tests in mice, Swiss researchers launched a clinical trial involving nine women diagnosed with metastatic breast cancer. At the start of the trial, all participants had at least one cluster of circulating tumor cells detected during screening.

For seven days, the participants took daily doses of digoxin. Researchers collected blood samples before treatment, two hours after the first dose, and again on days three and seven to monitor the circulating tumor cells.

The results were promising: the average number of cells per cluster dropped by 2.2 after treatment, down from an initial average of about four cells per cluster. Notably, no serious side effects were reported, further supporting the potential of this treatment.

What’s next for this discovery?

While the results are promising, experts Daniel Smit and Klaus Pantel from the University Medical Center Hamburg-Eppendorf in Germany point out some limitations. Although digoxin’s effect was statistically significant, it was still relatively modest.

The reduction in circulating tumor clusters could help lower the risk of future cancer spread, but it likely wouldn’t affect secondary tumors that have already formed. As a result, this medication may be most effective at a specific stage of cancer progression.

The researchers also noted that digoxin doesn’t stop circulating tumor cells from clumping with healthy blood cells, which also plays a role in cancer spread. And while breaking up these clusters could slow metastasis, individual tumor cells can still be harmful.

Given the wide variability in outcomes for metastatic breast cancer, the researchers view this finding from just nine patients as a promising starting point, not a definitive conclusion.

The research team is now working on developing new, more effective compounds based on digoxin to target circulating tumor clusters. They’re also investigating whether this approach could be effective against other types of cancer.

Marie Pireddu

Marie Pireddu is a French-English translator specializing in digital marketing, technology, and mobile apps. She is also a business English trainer for professional adults, helping clients master English for international business, with a focus on American culture and corporate communication.