Fast forward yet another century, and scientists started noticing some unexpected benefits of aspirin on preventing cardiovascular disease – reducing the risk of blood clots by making the blood thinner and the blood platelets less sticky. For this reason, organizations like the UK’s National Health Service recommend low daily doses for people with a high risk of heart attack or stroke.
By 1972, the potential benefits had extended to the prevention of cancer, with an attention-grabbing study of mice injected with tumorous cells. The American scientists found that lacing the animal’s drinking water with aspirin significantly reduced the risk that the cancer would spread across the body – a process called metastasis – compared to mice who were not given the drug.
While discovery generated some excitement, “it wasn’t immediately clear how this would impact clinical practice,” says Ruth Langley, a professor of oncology and medical trials at University College London. It wasn’t obvious if the drug would have the same effect in humans, after all – meaning that the finding remained an obscure fascination rather than a potentially life-changing treatment.
A turning point came in 2010, when Peter Rothwell, a professor of clinical neurology at the University of Oxford in the UK, went back and re-investigated the much more abundant data on aspirin as a prevention of cardiovascular disease. In his analyses, the drug appeared to reduce both the incidence and spread of cancer, prompting renewed interest in both the power of aspirin to help fight the disease, and the reasons that it does so.
Proving that aspirin can prevent cancer in the general population is a challenge, however. In an ideal world, researchers would recruit a large sample of people. Half would take aspirin, while the rest would take a placebo pill – and you would then compare which had the highest rates of the disease. It can take many decades for cancer to occur in the first place, however, meaning that a randomised controlled trial would take a very long time to conduct at a huge expense. “It’s almost impossible, actually,” explains Anna Martling, a professor of surgery at the Karolinska Institute in Sweden.
For this reason, scientists have turned their attention to specific groups, such as those who have already had cancer or those who are genetically susceptible to developing it.
Mounting evidence
It is here that John Burn’s study of patients with Lynch Syndrome, which vastly increases the risk of colorectal and other forms of cancer, enters the picture. In 2020, Burn published the results of a landmark randomized controlled trial of 861 patients with the condition. Following the participants for 10 years, his team discovered that people who had taken a daily 600mg dose of aspirin for at least two years effectively halved their risk of colorectal cancer.
His team have since conducted a second trial, which is currently under peer review. The early results suggest that a much lower dose of aspirin (75-100mg) is just as effective – if not more. “The people who took aspirin for two years had 50% fewer cancers in the colon,” he says. “What we want to do is keep on going for a few more years because the data is going to get better as time goes on.” (Nick James, the very first patient to enter the trial, was among the ones who appeared to have benefited.)
Aspirin appears to reduce the risk of colon cancer among those with a high genetic risk
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