Routinely taking aspirin increases the risk of developing bowel cancer for one in 25 people, a study has suggested.
Previous research has hailed the benefits of the drug in reducing cases of certain types of cancer, as well as helping to guard against heart attacks and strokes.
However, a review of studies involving 19,000 Europeans concluded that whereas regular use of aspirin cut the risk of developing bowel cancer in most people, its benefits differed depending on a person’s genetic make-up.
Among those with two less-common genotypes, accounting for one in nine people, aspirin appeared neither to increase nor reduce the risk of the disease. For those with two rare genotypes, accounting for one in 25 people in the study, aspirin use was associated with a higher risk of bowel, or colorectal, cancer.
The American researchers, writing in the journal JAMA, said the findings could be used to help to identify those who would benefit most from taking aspirin and non-steroidal anti-inflammatory drugs (NSAIDs) to reduce their risk of bowel cancer.
Routine use of aspirin or NSAIDs by those who are not unwell is not officially recommended because of uncertainty about the side-effects. For example, aspirin, which thins the blood, is already known to increase the risk of internal bleeding.
Dr Andrew Chan and colleagues at Massachusetts General Hospital in the US conducted a genome-wide analysis of the link between regular use of aspirin and NSAIDs and colorectal cancer. They used figures from five studies all involving people of European descent.
The team found that the benefits differed according to genetic variations running through the population. They added that the mechanisms behind the association were not well understood.
Dr Chan said: “Validation of these findings in additional populations may facilitate targeted colorectal cancer prevention strategies.”
Bowel cancer is Britain’s second biggest cancer killer, responsible for around 16,000 deaths each year.
More than 40,000 people are diagnosed with the disease each year, making it the fourth most common form of cancer.