Adenomatous polyps — Two-thirds of colon polyps are adenomas (hence the polyp is termed "adenomatous"). Most of these polyps do not develop into cancer but they do have the potential to become malignant. Adenomas are classified by their size, general appearance, and their specific features as seen under the microscope. As a general rule, the larger the adenoma, the more likely it is to eventually become a cancer. In addition, large adenomas may already have cancer contained within them. As a result, your doctor will usually try to biopsy (obtain a sample) or remove the polyp so that it can be examined under the microscope.