Polyp (tumor), benign or malignant tumor projecting above normal tissue surface level. Polyps are usually found protruding from an inner wall in the cavity of a hollow organ of the body, such as the stomach, colon, rectum, bladder, uterus, or larynx. There are several types of polyps. They may be inflammatory, meaning they rise at the focal point of an inflammation;
hyperplastic, resulting from an excessive increase in the number of normal cells; or neoplastic, meaning caused by an abnormal growth of new tissue. Inflammatory and hyperplastic polyps are benign and do not become cancerous, but neoplastic polyps can be either benign or cancerous.
Polyps also differ in the way they are connected to tissue surface. They can either be pedunculated (attached by a well-defined thin stalk) or sessile (arising on a broad base). Polyps are further classified by their microscopic cellular appearance. They can appear tubular (cells formed into tubelike structures), villous (with many tiny threadlike projections), or tubulovillous (a combination of both tubular and villous). Most benign polyps are small, typically less than 1 cm (0.5 in) in diameter, and produce no symptoms, but larger ones may bleed or produce mucus. Malignant polyps may consist partly or entirely of cancerous cells. Cancerous cells have the potential to metastasize, or spread to other organs of the body, and the likelihood of this spread increases with the size of the polyp, the absence of a stalk, and a villous shape. Most colon and rectal cancers are believed to arise from polyps.
When a polyp is discovered, it is important to identify its microscopic type, which can be done by biopsy (removal of a small piece of tissue) or excision (total removal of the polyp). Most benign—and many malignant—polyps occurring in the colon or rectum can be removed with a colonoscope (a long, flexible viewing device fitted with cutting or current-carrying instruments). Polyps too large to remove with a colonoscope or located in an area inaccessible to a colonoscope are removed by surgery.