We’ve gotten a lot better at fighting cancer, but there’s still a way to go. An important realization was that it’s not the primary tumor that often claims lives — it’s the spread of cancer to other organs, known as metastasis. Previous studies reported that a daily low-dose aspirin can lead to a reduction in the spread of some cancers, such as breast, bowel, and prostate cancers. Now, researchers have uncovered how this works.

Essentially, aspirin can boost the immune system’s ability to fight cancer metastasis by stopping platelets — tiny blood cells that help with clotting — from suppressing T cells, the body’s natural cancer fighters. However, researchers caution that aspirin can have serious side effects and people shouldn’t just start taking it willy-nilly.

Protect the troops

T cells are the body’s frontline soldiers against infection and disease. This also includes cancer. However, cancer has its ways of tricking T cells. When cancer cells enter the bloodstream and attempt to spread, platelets come to their defense. Platelets release a molecule called thromboxane A2 (TXA2), which shuts down T cell activity, making it easier for cancer to take root in new locations.

In the new study, researchers screened 810 genes in mice, finding that 15 of these genes have an effect on metastasis. In particular, mice lacking a gene that produces a particular protein had less metastasis in various types of cancer. This protein is called ARHGEF1, and it’s also linked with TXA2.

When TXA2 binds to T cells, it activates ARHGEF1, which then suppresses T cell activity. In experiments where researchers genetically removed ARHGEF1 from mice, their immune systems were much better at fighting metastatic cancer. This was the missing puzzle piece.

Aspirin reduces the production of TXA2, leading to the anti-clotting effects that underlie its ability to prevent heart attacks and strokes.

“It was a Eureka moment when we found TXA2 was the molecular signal that activates this suppressive effect on T cells,” said Jie Yang, one of the study authors from the University of Cambridge. “Before this, we had not been aware of the implications of our findings in understanding the anti-metastatic activity of aspirin. It was an entirely unexpected finding which sent us down quite a different path of inquiry than we had anticipated.”

Could aspirin become a weapon versus cancer?

The researchers emphasize that you shouldn’t just go out and take aspirin. This is far from confirmed in humans and we don’t yet have a treatment regimen. However, this study on mice fits with what we observed in humans. This suggests aspirin’s power isn’t just about reducing inflammation — it’s also an immune-boosting weapon. By stopping TXA2 from activating ARHGEF1, aspirin effectively removes the brakes on T cells. This allows them to do what they do best: hunt and destroy cancer.

This is particularly important with the recent progress in immunotherapy. Unlike other approaches like radiotherapy or chemotherapy, where external treatments are applied, immunotherapy focuses on supporting patients’ immune systems to fight cancer.

“Most immunotherapies are developed to treat patients with established metastatic cancer, but when cancer first spreads there’s a unique therapeutic window of opportunity when cancer cells are particularly vulnerable to immune attack. We hope that therapies that target this window of vulnerability will have tremendous scope in preventing recurrence in patients with early cancer at risk of recurrence,” says co-author Rahul Roychoudhuri, also from the University of Cambridge.

If confirmed, this discovery also opens the possibility of other, more focused treatments. Why use aspirin which works as a side effect when you can use a pill that focuses the problem exactly? Future therapies could include selective TXA2 inhibitors that don’t have other platelet functions or medications that prevent ARHGEF1 from shutting down T cell activity. Ultimately, aspirin or more refined pills could be combined with modern immunotherapy, although we’re not there quite yet.

Journal Reference: Rahul Roychoudhuri, Aspirin prevents metastasis by limiting platelet TXA2 suppression of T cell immunity, Nature (2025). DOI: 10.1038/s41586-025-08626-7. www.nature.com/articles/s41586-025-08626-7