The risk is greatest among the one in 25 people with a genetic predisposition for the cancer, which aspirin appears to activate. These people have two rare genotypes that interact with the painkiller and increase the likelihood for bowel, or colorectal, cancer.
Bowel cancer is the second most lethal form of the disease, and is responsible for 16,000 deaths in the UK alone each year. More than 40,000 Britons are diagnosed with the disease each year, making it the fourth most common type of cancer.
Researchers from the Massachusetts General Hospital discovered the risk when they profiled the health of around 19,000 Europeans taking aspirin. The findings point to the need for better profiling of patients, so that doctors can know who can safely take aspirin.
Although many doctors recommend we should be taking an aspirin a day, it has never become official health policy because of the drug's side effects, and the increased risk for bleeding in the stomach.
(Source: Journal of the American Medical Association, 2015; 313(11): 1133-42)