Aspirin May Reduce Cancer Risk: Ongoing Research Explores How and Why
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After scientists discovered that aspirin, a 4,000-year-old medication commonly used to relieve pain, might prevent the formation or spread of tumors, many countries around the world have begun revising their health policies accordingly.
Nick James, a carpenter in the UK in his mid-40s, decided to undergo genetic testing after his mother died of cancer and several of his family members, including his brother, were also diagnosed with the disease. The test revealed a gene that increased his cancer risk.
Unexpectedly, he found support by participating in a clinical trial where he took aspirin daily. The study aimed to investigate aspirin’s potential to halt cancer progression.
People with Lynch syndrome, a hereditary condition caused by gene mutations, face a lifetime risk of bowel cancer ranging from 10% to 80%. James is currently doing well. Professor Jan Burn, a clinical genetics expert at Newcastle University leading the study, said, “James has been on aspirin for 10 years and has not developed cancer so far.”
Though it may seem incredible, aspirin has shown signs of preventing colorectal cancer from developing or progressing. Similar results were reported in a study last year.
Some countries have revised their drug regulations to prioritize aspirin as a preventive measure for those at risk (experts emphasize consulting a doctor before taking medication). Researchers are gradually uncovering the mechanisms behind this treatment’s efficacy.
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Ancient Origins
A new study highlights the long history of a remarkably effective medicine. In the late 19th century, archaeologists unearthed 4,400-year-old clay tablets in the Mesopotamian city of Nippur, now in Iraq. These tablets contained lists of medicines derived from plants, animals, and minerals.
They even described methods to extract sap from willow trees.
It is now known this sap contains salicin, which converts to salicylic acid in the body and helps reduce pain. This compound closely matches the chemical structure of modern aspirin, scientifically known as acetylsalicylic acid. The medicine was also used in ancient Egypt, Greece, and Rome.
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This modern compound was studied by English chemist Edward Stone, who presented his findings on willow bark powder’s fever-reducing effects to the Royal Society. A century later, scientists isolated salicylic acid from that powder and then converted it into acetylsalicylic acid, introducing aspirin commercially under brand names.
In the following century, researchers discovered aspirin’s unexpected benefits for heart disease. Institutions like the UK’s National Health Service now recommend a low daily dose of aspirin to reduce the risk of heart attacks and strokes.
By 1972, initial evidence suggested aspirin might protect against cancer. At that time, mice injected with tumor cells were given water mixed with aspirin. These mice showed a lower risk of developing cancer compared to those without aspirin in their water.
Whether the same effect would hold true in humans remained uncertain.
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A turning point came in 2010 when Professor Peter Rothwell from Oxford University’s Clinical Neurology department showed how aspirin provides benefits in heart disease. His study also revealed aspirin’s dual role: both preventing and slowing cancer growth.
Confirming aspirin’s protective effect against cancer in the general population remains challenging, requiring large trials where half the participants receive aspirin and the other half a placebo, monitoring outcomes over prolonged periods at significant cost. Surgeon Professor Anna Martling of Sweden’s Karolinska Institute remarked, “It’s hard to imagine such an ideal study.”
Consequently, research has largely centered on individuals with precancerous conditions or high-risk profiles.
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Growing Evidence
A significant study involved patients with Lynch syndrome. In 2020, Jan Burn and his team conducted a controlled trial with 861 participants. Those who took 600 mg of aspirin daily for ten years had their risk of colorectal cancer reduced by half.
Ongoing trials suggest that even lower doses (75–100 mg) may also be effective.
Burn explained, “A 50% reduction in colorectal cancer risk has been observed after two years of aspirin use.”
Low-dose aspirin (75–100 mg) is already prescribed to the general population to prevent heart disease. However, aspirin can cause digestive issues, internal bleeding, and brain hemorrhages, so dosage requires careful management.
Following this research, guidelines have been updated. Burn noted, “According to this study, UK guidelines now recommend aspirin starting at age 20 for individuals with Lynch syndrome, and from 35 for those at lower risk.”
Research has also started to explore aspirin’s benefits across other patient groups.
Trials continue investigating whether aspirin decreases metastasis risk in patients already diagnosed with cancer. Martling commented, “Approximately 40% of colorectal cancer patients have mutations where aspirin may be beneficial.”
A three-year trial involving 2,980 participants found that those who took 180 mg of aspirin within three months post-surgery had less than half the risk of cancer recurrence compared to the placebo group. Both Martling and Burn report minimal serious side effects with aspirin use.
Following publication of Martling’s study in September 2025, Sweden promptly revised its protocols, beginning low-dose aspirin for bowel cancer patients from January 2026.
It remains unclear if aspirin protects against other types of cancer. However, trials including 11,000 patients in the UK, Ireland, and India with colorectal, breast, gastroesophageal, and prostate cancers are underway, with results expected next year.
How Does Aspirin Work?
The exact mechanisms by which aspirin prevents cancer remain mysterious. Martling explains the drug acts both inside and outside cells, potentially activating various internal processes.
Her research indicates aspirin inhibits the enzyme COX-2 inside cells, which produces compounds called prostaglandins that may promote uncontrolled cell growth. By suppressing COX-2, aspirin might curb this excessive proliferation.
Additional work by Professor Rahul Roychoudhury and colleagues at the University of Cambridge suggests aspirin may also help destroy metastatic cancer cells through other pathways.
Determining who should take aspirin regularly remains a topic of debate. Some researchers advocate widespread use for protection against both heart disease and cancer. Burn views aspirin’s role in public health with optimism.
However, some scientists caution that while aspirin may benefit cancer patients, healthy individuals taking it independently might suffer harm due to serious side effects. Additionally, aspirin’s effectiveness varies among cancer patients.
* This article provides general information and is not a substitute for medical advice. No responsibility is taken for any individual’s medical decisions based on this information. No commercial endorsements are made here. If you have health concerns, please consult a qualified doctor.