Researchers previously were aware that non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin could reduce colorectal cancer risks, but they did not understand why some saw a benefit and others did not, according to the study in Science Translational Medicine.
Scientists studied tissues from people who developed colon cancer while on an aspirin regimen then set out to understand why people with a particular gene appeared to get a protective benefit from aspirin and others did not.
They examined tissues of 270 colon cancer patients from 127,865 participants followed for over three decades.
They found that patients who lacked a genetic profile which yields high levels of the enzyme 15-PGDH got almost no protective benefit for colon cancer from aspirin.
"If you looked at the folks from the study who had high 15-PGDH levels and took aspirin, they cut their risk of colon cancer by half," said senior author Sanford Markowitz of Case Western Reserve School of Medicine.
Yet "if you looked at the folks from the study that were low for 15-PGDH, they did not benefit at all from taking aspirin. These findings represent a clean yes-no about who would benefit from aspirin," he explained.
Identifying who can benefit from the colon cancer-reducing potential of aspirin is an important step because in some patients aspirin causes an increased risk of stomach ulcers and gastrointestinal bleeding, researchers said.
They are hoping to develop a test that would make it easy to identify who is and is not likely to get the positive effects of aspirin.
According to the American Cancer Society, colon cancer struck 137,000 Americans in 2014 and 50,000 will die of it. It is the second deadliest cancer after lung cancer.
But colon cancer deaths have been decreasing steadily over the past two decades as more and more people have sought testing, particularly colonoscopies.