A new pair of studies suggests that a daily dosage of aspirin for at least five years reduces the risk of cancer.
Aspirin is one of the oldest medicines in human history. In 400 B.C Hippocrates prescribed willow bark containing aspirin. to Greek women to reduce pain during childbirth. In 1897 Bayer's Felix Hoffman develops a method for developing aspirin synthetically. Although aspirin is normally taken as a painkiller, it has been found to prevent other diseases including cardiovascular disease and, most recently, a variety of cancers. Aspirin acts as a blood thinner, this is the mechanism by which it reduces risk of stroke and heart attack.
Mounting evidence suggests that taking aspirin on a daily basis reduces cancer risk. A team lead by Professor Peter M. Rothwell out of the University of Oxford has been grabbing headlines with studies providing strong support for aspirin's ability to reduce cancer risk. At the end of 2010 they found by combing through aspirin and heart disease correlational studies that a daily dosage of aspirin reduced long-term risk of developing pancreatic, esophageal, brain, stomach, colorectal and prostate cancers (Effect of daily aspirin on long-term risk of death due to cancer: analysis of individual patient data from randomized trials, 2010, P Rothwell, et al.). The study found that long-term reductions in cancer risk were apparent in subjects who took daily aspirin treatment for at least five years, but the risk-reduction was greater for subjects who took a daily aspirin treatment for more than 7.5 years. In addition, daily aspirin dosages exceeding 85 mg did not appear to reduce relative cancer risk. Additionally, as demonstrated by the figures below, the disparity between the control group and the aspirin dosage experimental group did not appear until 5 to 20 years following the conclusion of the study.
The analysis also found that subjects over 65 years of age saw a greater absolute reduction in cancer risk. Another interesting finding was that subjects only saw a reduction in cancer risk if they had been on a daily dosage schedule. Alternate daily dosages did not reduce cancer risk. This suggests that the mechanism by which cancer risk is reduced is not the irreversible inhibition of cox-2 (an enzyme responsible for pain and inflammation that is targeted by aspirin).
Another study, published in 2012 by the same team looked at short-term cancer risk reduction ( 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, 2012, Peter M Rothwell, et al.). This study found that after a five year delay, cancer mortality was reduced by 40%. Cancer incidence was reduced by 25% after a three year follow-up.
One of the major drawbacks of taking a daily dosage of aspirin is an increase in risk of extracranial bleeding and hemorrhages. The researchers addressed this in their second study. On the short-term, mortality attributed to vascular disease was not affected and the increase in mortality do to fatal hemorrhaging was more than offset by the reduction in cancer risk. In addition, for non-gastrointestinal cancers, risk reduction was correlated with age.
In summary, these studies show a correlation between reduced cancer risk in all fatal cancers and daily aspirin administration. The reduction in cancer mortality lowers overall mortality, even when factoring aspirin-induced risks such as hemorrhaging.