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

A century-old heart medication derived from the foxglove plant could revolutionize how we treat cancer. Swiss researchers have discovered that digoxin can dissolve clusters of circulating cancer cells, potentially preventing their spread throughout the body. This promising finding could open a new therapeutic avenue against metastasis, which is responsible for most breast cancer–related deaths.

Breast cancer remains one of the leading causes of death among women in the United States, mainly because of its ability to spread to other organs. Current treatments focus primarily on destroying tumor cells but don’t specifically target the metastatic process. A recent study published in February 2025 in Nature Medicine suggests that a century-old heart drug might offer a complementary approach by stopping cancer cells from dispersing.

How digoxin is changing the understanding of metastasis

Digoxin, a medication extracted from Digitalis lanata in 1930, has traditionally been used to treat heart failure and atrial fibrillation. It works by blocking the sodium-potassium pumps in cardiac cells, leading to stronger contractions and a slower heart rate.

That same mechanism may now have an unexpected use in cancer treatment. By inhibiting these pumps in tumor cells, digoxin increases calcium intake. Previous studies have shown that this rise in calcium disrupts the formation of tight junctions and desmosomes—structures that are essential for cell adhesion.

Circulating tumor cells play a crucial role in the formation of metastases. When these cells group together, their likelihood of creating new tumors in distant organs rises sharply. Digoxin weakens the bonds between these cancer cells, promoting the disintegration of such clusters and potentially limiting their ability to invade new tissues.

Encouraging first results in humans

Following successful mouse experiments, Swiss researchers conducted a clinical trial involving nine women with metastatic breast cancer. Each participant had at least one cluster of circulating tumor cells identified during the initial screening.

During the study, participants took digoxin daily for seven days. To monitor changes in circulating tumor cells, blood samples were collected before treatment, two hours after the first dose, and again on days three and seven.

The results showed an average reduction of 2.2 cells per cluster after treatment, compared to an average of four cells before intervention. No serious side effects were reported, strengthening the case for this therapeutic approach.

Perspectives and limitations of this discovery

Despite the encouraging results, medical experts Daniel Smit and Klaus Pantel from the University Medical Center Hamburg-Eppendorf in Germany emphasized several limitations in their commentary on the study. While digoxin’s effect was statistically significant, it remained relatively modest.

In theory, reducing circulating clusters could lower the risk of future cancer spread, but it probably wouldn’t halt the growth of already established secondary tumors. The drug may therefore be most effective at a specific stage of cancer progression.

Experts also noted that digoxin doesn’t prevent circulating tumor cells from aggregating with healthy blood cells—a process that also contributes to the spread of cancer. Moreover, although breaking up clusters could slow metastasis, single circulating tumor cells are also known to have negative effects.

Given the variety of clinical outcomes among metastatic breast cancer patients, researchers view this finding—based on nine individuals—as a promising hypothesis rather than a definitive conclusion.

The research team now plans to design new molecules derived from digoxin that may prove even more effective at breaking apart circulating clusters. Additional experiments are underway to determine whether this approach could apply to other types of cancers as well.