A combined analysis of 51 randomized trials found that daily aspirin use reduces the risk of new cancer diagnoses as well as the risk of cancer death. These results were published in The Lancet.
A growing body of evidence suggests that aspirin may reduce the risk of several types of cancer, with particularly strong evidence for colorectal cancer. Not all studies have found a benefit, however, and any potential benefits of aspirin must be weighed against risks such as bleeding.
To further explore the relationships between daily aspirin and cancer, researchers conducted a combined analysis of 51 previous randomized trials. The trials were originally designed to evaluate the effect of daily aspirin on outcomes such as heart disease, but information about cancer was also available.
- Daily aspirin reduced cancer deaths. After five years, aspirin users had a 37 percent reduction in risk of cancer death.
- Aspirin also reduced the likelihood of developing cancer. From three years onward, aspirin users had a 24 percent reduction in the risk of being diagnosed with cancer.
- As expected, aspirin carried a risk of major bleeding, but this risk appeared to diminish over time.
Another study published in the same issue of The Lancet evaluated the effect of daily aspirin on cancer metastasis (the spread of cancer from its original site to other parts of the body). The study focused on 987 people who were diagnosed with cancer while participating in one of five trials of aspirin use. Those who were taking aspirin were less likely to have metastatic cancer than those who were not taking aspirin.
These results suggest that regular aspirin use may reduce cancer incidence and mortality, but concerns remain about the risks of regular aspirin use in healthy individuals. People who are considering using aspirin on a regular basis are advised to discuss the risks and benefits with their physician.
 Rothwell PM, Price JF, Fowkes FGR et al. Short-term effects of daily aspirin on cancer incidence, mortality, and non-vascular death: analysis of the time course of risks and benefits n 51 randomised controlled trials. Lancet. Early online publication March 21, 2012.
 Rothwell PM, Wilson M, Price JF, Belch JFF, Meade TW, Mehta Z. Effect of daily aspirin on risk of cancer metastasis: a study of incident cancers during randomised controlled trials. Lancet. Early online publication March 21, 2012.