The mortality reducing effect of aspirin in colorectal cancer patients: Interpreting the evidence

In 1971 the first study appeared that suggested a relationship between aspirin and cancer. Currently publications on the subject of aspirin and cancer are numerous, with both a beneficial effect of aspirin on cancer incidence and a beneficial effect on cancer survival. This review focusses on the relation between the use of aspirin and improved survival in colorectal cancer patients. Various study designs have been used, with the main part being observational studies and post hoc meta-analyses of cancer outcomes in cardiovascular prevention trials. The results of these studies are unambiguously pointing towards an effect of aspirin on colorectal cancer survival, and several randomised controlled trials are currently ongoing. Some clinicians feel that the current evidence is conclusive and that the time has come for aspirin to be prescribed as adjuvant therapy. However, until this review, not much attention has been paid to the specific types of bias associated with these studies. One of these biases is confounding by indication, because aspirin is indicated for patients as secondary prevention for cardiovascular disease. This review aims to provide perspective on these biases and provide tools for the interpretation of the current evidence. Albeit promising, the current evidence is not sufficient to already prescribe aspirin as adjuvant therapy for colorectal cancer.