These form a small proportion of all colonic
polyps. Doctors remove adenomas because some of them may progress to colon cancer.
It is difficult to tell by external appearance whether a polyp is an adenoma. The diagnosis is made by microscopic appearance. The majority of adenomas are benign and the very act of removing them during colonoscopy is sufficient to eliminate the risk of cancer developing in that polyp. Only a very small number of cases need surgery.