Abstract

Evidence from observational studies has suggested for several decades now that aspirin might reduce the long-term incidence of some cancers, particularly of the gastrointestinal tract. Long-term follow-up of randomised trials of daily aspirin versus control in prevention of vascular events has recently shown that aspirin does indeed reduce incidence of colorectal cancer after a delay of 8-10 years,^1,2 and that it reduces deaths due to other gastrointestinal cancers and possibly lung cancer.³

There is also some evidence that aspirin improves outcome in patients who develop cancer whilst on treatment. The short-term effect of aspirin on deaths due to cancer is larger than the effect on incidence and the effect on mortality occurs too quickly to be reasonably be explained by an effect only on carcinogenesis or early cancer growth.⁴ In keeping with evidence that platelets play an important role in blood borne metastasis, in five large randomised trials of aspirin vs control in prevention of vascular events randomisation to aspirin reduced rates of metastasis in participants with a new diagnosis of cancer during follow-up.⁵ Consistent evidence of similar effects on distant metastasis and outcome have also been reported in observational studies.⁶

These findings are encouraging, but questions remain. In relation to cancer prevention, for example, most of the randomised trials studied so far included mainly men, although 17-year follow-up in the Womens Health Study did recently show consistent effects in women. Similarly, although evidence of effects of aspirin on risk of gastrointestinal cancers is now substantial, more data are required on other cancers and the optimal dose of aspirin for long-term prevention of cancer remains uncertain. The NOn-Vascular outcomes on Aspirin (NOVA) Collaboration has been established to collate all data from previous and ongoing trials of aspirin in order to provide as reliable data as possible on short-term and long-term effects of aspirin.

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2. Rothwell PM, Wilson M, Elwin CE, Norrving B, Algra A, Warlow CP, Meade TW. Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomised trials. Lancet 2010; 376: 1741-50.

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4. Rothwell PM, Price JF, Fowkes FG, Zanchetti A, Roncaglioni MC, Tognoni G, Lee R, Belch JF, Wilson M, Mehta Z, Meade TW. Short-term effects of daily aspirin on cancer incidence, mortality, and non-vascular death: analysis of the time course of risks and benefits in 51 randomised controlled trials. Lancet 2012 ;379:1602-12.

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