For decades, aspirin has been known as a go-to painkiller. New research reveals how it may also help fight cancer.

While previous research hinted at a link between aspirin use and improved cancer survival, a study published in Nature last week explains why. However, experts caution that aspirin is not a cure – and it carries risks like increased potential for internal bleeding.

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So, how might aspirin keep cancer from spreading? And what does this mean for future treatments?

What have studies found about aspirin use and cancer?

Recent studies have revealed how aspirin, a widely used painkiller, may help prevent the spread of cancer, although it is unclear whether it would work the same for all types of the disease.

Researchers have been exploring this link for decades. The first clinical study, published in 1988, showed that regular aspirin use significantly lowered the risk of colorectal cancer, though the underlying reason remained unclear.

Now, a new study from the University of Cambridge offers more insight. It found the mechanism by which aspirin may help prevent cancer from spreading, a process known as metastasis.

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Metastasis is responsible for the majority of cancer-related deaths, as cancer cells break away from the original tumour and try to take root elsewhere​ across the body.

As these drifting cancer cells go rogue, aspirin may enhance the body’s natural ability to fight back, keeping the cancer cells from taking hold of more organs.

How can aspirin keep cancer from spreading?

The key to aspirin’s effect on cancer lies in the body’s immune system, a complex network of cells and proteins that defends against infections, diseases and harmful germs.

When cancer cells break away from a tumour, they enter the bloodstream, where the immune system – specifically types of white blood cells known as T-cells – normally hunts them down and destroys them. However, platelets – tiny cell fragments in the blood that help with clotting – can interfere with this process.

Cancer takes advantage of platelets by triggering a response similar to an injury. When platelets detect the free-floating cancer cells, they rush to coat them, much like they would cover a wound to stop bleeding.

This creates a protective shield, making it harder for the immune system to recognise and attack the cancer cells. Additionally, platelets release signals that suppress T-cells, preventing them from doing their job.

Aspirin disrupts cancer’s attempts at trickery by reducing the production of a molecule that platelets use to suppress immune activity. With the platelets weakened, T-cells regain their ability to recognise and destroy cancer cells before they have a chance to form new tumours.

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How could aspirin be used against cancer?

The study suggests that aspirin could be used after treatments like surgery where tumours are removed.

This is because some cancer cells may have already escaped from the tumour and begun to settle in other parts of the body, a process known as seeding, where tiny cancer cells embed themselves in new areas and may later grow into tumours.

However, experts caution against immediately using aspirin as a cancer treatment without further research. The painkiller carries the potential for serious side effects such as internal bleeding because by weakening the platelets, it can weaken their ability to help blood clot.

Aspirin blocks a molecule that prods platelets to clump together. This makes the blood thinner and increases the risk of uncontrolled bleeding. This is especially dangerous in the stomach, where aspirin can irritate the lining and cause ulcers, and in the brain, where it raises the risk of a hemorrhagic stroke if a tiny blood vessel bursts.

Additionally, the study was carried out on mice, not humans, so its effects on cancer spread still need to be confirmed before it can be recommended for treatment.

“Our research provides a molecular explanation for observations from clinical studies, but proper clinical validation is still needed,” Rahul Roychoudhuri, a professor in Cambridge’s Department of Pathology who was part of the Nature study, told Al Jazeera.

Several clinical trials, such as the ADD-ASPIRIN trial in the United Kingdom, Ireland and India, are under way to determine which patients are most likely to benefit most from taking aspirin and whether it works for specific types of cancers.

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Roychoudhuri added that he does not anticipate an “immediate fast-tracked translation” of aspirin to cancer treatment.

Has aspirin been used against diseases in the past?

Some patients with a high genetic risk for cancer, such as those with Lynch syndrome (a condition that increases the likelihood of developing certain cancers), are already recommended aspirin as a preventive measure​ in countries such as Australia and the UK.

Since the 1980s, aspirin has also been prescribed to help prevent heart attacks and strokes in people at high risk of heart disease, by reducing the ability of platelets to form harmful clots that can block blood flow to the heart or brain. This clot-preventing effect helps lower the risk of heart attacks in those with a history of cardiovascular disease.

Does this mean we are close to a breakthrough in curing cancer?

Not necessarily. While aspirin may help slow or prevent the spread of cancer, it does not eliminate tumours entirely.

However, scientists are working to identify biomarkers – measurable signs in the blood – and platelet activity to help detect individuals at risk for cancer early on.

“This would allow for timely treatment with aspirin while minimising unnecessary exposure for those who do not require it,” said Paola Patrignani, a professor of pharmacology at Gabriele d‘Annunzio University in Italy.

Experts say the findings could also contribute to the development of drugs that inhibit cancer spread.

“Our discoveries open possibilities for developing more targeted therapies that could potentially provide the benefits without aspirin’s side effects,” Roychoudhuri said.

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Patrignani, who is involved in research funded by Cancer Research UK to investigate whether other anti-platelet drugs, like clopidogrel, might offer similar benefits, says these studies will require another three to five years to be completed.

However, she is optimistic about where the research is heading. “We are on the verge of a significant breakthrough in cancer research. This newfound knowledge could pave the way for innovative treatments and potentially save countless lives.”

Why does a cure for cancer remain so elusive?

Finding a cure for cancer remains one of the greatest challenges in medicine.

As there are many different types of cancer, each with its own characteristics and ways of spreading, it is difficult to develop a universal cure.

Additionally, tumour development is influenced by a combination of genetic predisposition and environmental factors. Studies suggest that treatment must be personalised to be truly effective.

Many cancers also develop ways to hide from or suppress the immune system, making them harder to attack even with immunotherapy.