A drug that has been in medicine cabinets for over a century may also be one of the most powerful tools we have against cancer. The link between Aspirin and cancer risk has been studied for decades but a landmark study published in Nature in March 2025 has finally explained the biological mechanism behind it.
The discovery changes how scientists think about cancer prevention and opens the door to a new generation of anti-cancer treatments inspired by one of the world’s oldest medicines.
What the Research Found
The breakthrough came from scientists at the University of Cambridge, who were studying how cancer spreads or metastasises through the body. They found that blood platelets produce a clotting compound called thromboxane A2, or TXA2, which plays a previously unknown role in suppressing the immune system’s ability to fight spreading cancer cells. Specifically, TXA2 switches on a protein called ARHGEF1 inside T cells the immune system’s frontline cancer killers effectively disabling them. When aspirin blocks the enzyme that produces TXA2, those T cells are freed to do their job. The result, in animal studies, was a significant reduction in metastasis to the lungs and liver.
How Aspirin Works Against Cancer
Understanding Aspirin and cancer risk requires understanding what aspirin actually does in the body. Aspirin blocks an enzyme called cyclooxygenase-1 known as COX-1 which platelets use to produce TXA2. Low-dose aspirin, typically 75 to 100 mg daily, permanently inactivates COX-1 in platelets for the lifetime of that platelet. This suppresses TXA2 production, which in turn prevents the immune-suppressing chain reaction that allows cancer cells to slip past the body’s defences. Scientists describe this as converting a “cold” tumour environment one where the immune system is shut out into a “hot” one where T cells can infiltrate and attack. This is the same goal pursued by expensive antibody-based immunotherapy drugs, at a fraction of the cost.
Can Aspirin Stop Cancer Spreading?
The question of whether can aspirin stop cancer spreading is now backed by a clear biological answer. The 2025 Cambridge study demonstrated in animal models that restricting TXA2 through aspirin reduced the rate of metastasis in multiple cancer types. Earlier population studies had already observed that people taking daily low-dose aspirin showed reduced spread of breast, bowel, and prostate cancers but scientists did not know why. Now they do. Metastasis is responsible for 90% of all cancer deaths globally, so targeting it effectively is arguably more important than preventing the initial tumour. The cancer prevention implications of this finding extend well beyond colorectal cancer, which has historically been the focus of aspirin research.
Colorectal Cance The Strongest Evidence
The strongest and most consistent evidence for Aspirin and cancer risk reduction comes from colorectal cancer. A 2025 study presented at the American Society of Clinical Oncology found that 160 mg of aspirin daily after treatment reduced colorectal cancer recurrence by 55% in patients with a specific genetic mutation called PI3K present in around 30% of colorectal cancers. A separate meta-analysis of over 260 studies involving 78 million individuals found a consistent association between regular aspirin use and lower cancer risk, particularly for colorectal and liver cancers. Research led by Harvard linked six or more years of aspirin use to a 19% reduced risk of colorectal cancer and a 15% reduced risk of gastrointestinal cancers overall.
PlateletsThe Key Connection
A parallel line of research from an international collaboration called SPARC Suppressing Platelet Activation to Reduce Cancer led by University College London and funded by Cancer Research UK, confirmed the platelet connection from a different angle. Their findings showed that low-dose aspirin suppresses platelet activation, which is responsible for preventing new tumours from growing and reducing the spread of cancer to other parts of the body. Activated platelets, the SPARC research found, increase inflammation, promote tumour growth, and block the immune system from removing cancer cells that have already spread. Aspirin interrupts this process at the source. The SPARC group is now bringing together clinical trial data from patients taking aspirin after cancer prevention treatment worldwide to identify who benefits most.
The Important Caveats
The Aspirin and cancer risk story is not without complications. A major 2026 study from Monash University found that for adults aged 70 and older, starting a programme of daily low-dose aspirin does not reduce long-term cancer incidence and may actually elevate cancer mortality risk in some cases. This aligns with earlier findings from the ASPREE trial, which showed that daily aspirin in older adults was associated with a moderately higher risk of advanced cancer. The scientific consensus is clear aspirin’s cancer prevention benefits appear strongest in middle-aged adults and may not apply uniformly across all age groups or cancer types. Aspirin can also cause serious side effects including gastrointestinal bleeding, which means it cannot be recommended as a blanket cancer prevention measure for everyone.
What Comes Next Clinical Trials and Future Drugs
The Cambridge discovery has energised ongoing clinical trials. The Add-Aspirin trial, led by UCL’s Professor Ruth Langley, is investigating whether aspirin can prevent early-stage cancers from returning after treatment and the 2025 mechanism discovery will help researchers interpret those results and identify which patients are most likely to benefit. More broadly, scientists believe the TXA2-ARHGEF1 pathway could be targeted by newer, more precise drugs that achieve aspirin’s anti-metastatic benefits without its bleeding risks. For the global majority of cancer patients who cannot access or afford expensive immunotherapy, a drug as cheap and widely available as aspirin offering genuine can aspirin stop cancer spreading benefits represents a potentially transformative development in oncology.
Frequently Asked Questions
Does aspirin kill cancer cells?
Aspirin does not directly kill cancer cells. Its role in Aspirin and cancer risk reduction works indirectly by blocking the COX-1 enzyme in platelets, which reduces TXA2 production, which in turn releases T cells from suppression, allowing the immune system to identify and destroy metastatic cancer cells. Aspirin empowers the body’s own immune defences rather than attacking cancer directly. This is why its effect on reducing cancer deaths is often greater than its effect on preventing the initial development of tumours.
Can aspirin stop cancer spreading?
The evidence that can aspirin stop cancer spreading is now supported by a clear mechanism. A 2025 Nature study showed that aspirin reduces metastasis the spread of cancer from the original tumour to other organs by freeing T cells from a suppressive pathway controlled by platelet-derived TXA2. Population studies have observed reduced spread of breast, bowel, and prostate cancers in people taking daily low-dose aspirin. However, clinical trials are still underway to determine safe dosing and to identify which patients benefit most. Anyone considering aspirin for this purpose should consult their doctor first due to potential side effects including gastrointestinal bleeding.
What is the aspirin cancer prevention dose?
Most research on Aspirin and cancer risk has been conducted using low-dose aspirin in the range of 75 to 100 mg daily. This dose permanently inactivates the COX-1 enzyme in platelets for the lifetime of each platelet, suppressing TXA2-dependent platelet activation. The 2025 ASCO colorectal cancer recurrence study used 160 mg daily. Standard-dose aspirin of 300 to 325 mg has also been studied but carries a higher risk of gastrointestinal bleeding. The optimal dose for cancer prevention has not yet been definitively established, and current guidelines do not recommend starting aspirin solely for cancer prevention without medical advice.
