The importance of these subtypes is that the villous adenoma has a greated malignant potential than the tubular adenoma.
Villous adenomas are sometimes responsible for diarrhoea and should be remembered if the patient has diarrhoea, particularly if they are hypo-kalemic.
On endoscopy the typical adenomatous polyp appears different from the surface of the surrounding bowel, they are often easier to see because of this. The malignant potential of adenomatous polyps is related to its size, it has been estimated that less than 1% of adenomatous polyps less than 1.2 cm in diameter are malignant.
For many years there was controversy about whether cancer arose in polyps or de-novo. It was postulated by some that polypoid cancers did not arise in a polyp but they just mimic one. Others postulated that most cancers do not look like a polyp because the cancer has overgrown and cannabalised the original polyp. It is clear that cancer is more common in people who have polyps and molecular studies show the same type of mutations found in cancers in polyps except there are less of them. The most commonly held belief is that polyps are one small step along the road to a cancer.