Smaller doses of aspirin work better than larger doses in reducing the risk of pre-cancerous growths in the colon, a group of Dartmouth researchers reported in the first study of its kind.
The research, which tested baby aspirin against standard adult aspirin in patients at increased risk for colon cancer, was presented at the 93rd annual meeting of the American Association of Cancer Research in San Francisco.
"The fact that we found activity in suppressing adenomas [pre-cancerous growths] is certainly very encouraging ... although we were very surprised by the fact that the smaller doses of aspirin worked better than the larger ones, and we don't really understand why," say study author Dr John Baron, a professor of medicine at Dartmouth Medical School.
Adenomas - also known as polyps - start out as benign growths that develop in the lining of the colon. Although not all polyps are considered adenomas, those that are, are believed to be precursors to cancer. If not removed, adenomas can become extremely aggressive, and they can eventually result in colorectal cancer.
Although epidemiology studies have long shown that aspirin may protect against colon cancer by reducing the risk of adenomas, this was the first study to examine which dosages might work best, particularly for those already at increased risk.
"Overall, we found that, in those people who already had one adenoma removed, aspirin definitely had a protective effect, and moreover, those who had the most aggressive adenomas had the greatest margin of protection, and from the smallest dose of aspirin," Baron says.
The aspirin doses used in the study were 80mg daily (the equivalent of one baby aspirin) and 325mg daily (equal to one standard aspirin). The dosages were chosen, says Baron, because they reflected what people were already taking for cardiovascular protection.
Protection without mass dosage
For gastroenterologist Dr Carl McDougall, that line of thinking makes good sense, and he calls the study finding important.
"Overall, this is a very good study with some very good news, because it means that people may be able to get the protective effects of aspirin, even if they are not able to take large amounts," McDougall says.
But he does note that because the study is a first to look at different doses, that automatically limits the impact of the finding.
"I'd like to see this kind of study confirmed independently . . . You really need to see these results duplicated before you can say for certain that lower doses work best for preventing these adenomas," says McDougall, an associate professor of clinical medicine at New York Weill Cornell Medical Centre.
And, he adds, because this study included only those people who already had had adenomas, it's hard to know whether the smaller doses would be equally effective in protecting against the initial development of these lesions, or if larger doses might work better for this group.