Over the last year or so there has been a number of well publicized studies linking aspirin with a reduction in the risk of developing various forms of cancer. Many people will be wondering if the decreased risk of cancer is sufficient to justify taking a low dose aspirin daily. While doctors normally recommend a low dose aspirin regime to prevent myocardial infarction in patients with pre-existing cardiovascular disease, most shy away from recommending low dose aspirin to apparently healthy individuals.
It is important for people to weigh up both the risks of daily low-dose aspirin (a marginally increased risk of gastrointestinal and intracranial bleeding) with the benefits (a decreased risk of heart attacks, ischemic strokes, and cancer). In the case of cancer, the ability of aspirin to reduce the risk of developing colorectal cancer has been known for some time however the effect of aspirin on other forms of cancer has been unclear.
That all changed in December of last year when a large meta-analysis of eight previous randomized control trials was published in the journal The Lancet. The study had several strengths over other studies of aspirin and cancer in that it involved a large number of patients (25 570 patients and 674 cancer deaths) and used data from randomized control trials (RCTs) rather than observational studies (which are more prone to confounding and other biases).
The results of the study made for some interesting reading. The risk of dying from cancer was reduced by 14% in the aspirin group over the first five years from trial commencement, however this increased to a massive 34% reduction in cancer deaths with at least five years of follow-up. The effect of cancer on the risk of death for a variety of cancer sites are shown on the graph below.
All major cancer sites, with the exception of stomach, and bladder and kidney cancers, showed reductions in mortality for the aspirin group vs control. Gastrointestinal cancers showed larger reductions in risk than other cancer sites. Results were particularly impressive for pancreatic and colorectal cancer which were reduced by 75% and 59% respectively (>5 years follow-up). Haematological cancers which includes leukaemias, lymphomas, and myelomas, were reduced by 66%, lung cancer by 32%, and prostate cancer by 48%.
The researchers also investigated the 20-year risk of cancer death for the aspirin group vs control. Interestingly, a significant reduction in cancer mortality remained at 20 years even though the trials had long since finished. The 20-year risk of cancer death in the aspirin group was 35% lower for gastrointestinal cancers and 20% lower for all cancers combined. The researchers also noted that the estimated reductions in 20-year cancer risk due to aspirin were likely to be under-estimated because some of the patients in the aspirin group would likely have stopped taking aspirin.
The authors concluded that “taking aspirin daily for 5–10 years would reduce all-cause mortality (including any fatal bleeds) during that time by about 10%”.
If a new drug entered the market that could potentially cut cancer deaths by a third and total mortality by 10% it would receive massive media coverage so it is somewhat surprising that more hasn’t been made of this study. The main reason cited by doctors as to why low-dose aspirin isn’t recommended routinely to adults is that it increases the risk of major bleeds in the stomach and inside the brain, however the increased risk is minimal and these bleeds rarely result in death. A 2006 study published in the American Journal of Medicine found that the absolute increase in major bleeding events as a result of aspirin was 0.12% per year for gastrointestinal bleeds and 0.03% per year for intracranial bleeds.
To sum up, given the impressive results of the above study, middle aged and elderly people without a history of gastric ulcers or bleeding should strongly consider taking a low-dose (75-150mg) of aspirin daily.
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