Colon polyp: A fleshy growth on the inside (the lining) of the colon (the large intestine). Colon polyps are extremely common. Their incidence increases as individuals get older. Half of all people over the age of 60 harbor at least one polyp. Polyps give rise to colon cancer, the second leading cause of death from cancer in the US. Screening for colon polyps and removing them before they become cancerous markedly reduces the incidence of colon cancer.

Colon polyps are more properly referred to as colorectal polyps since they occur in the rectum, too. Colorectal polyps are conventionally divided into two groups -- nonneoplastic polyps and neoplastic polyps (also called adenomatous polyps or adenomas). The nonneoplastic polyps have not been considered precursors (forerunners) of cancer while the neoplastic polyps are precursors of colorectal cancer.

Most adenomas of the colon are polypoid. However, flat and depressed adenomas may be more prevalent than has been thought. Large flat and depressed adenomas may be more likely to be severely dysplastic and give rise to malignancies.

Nonneoplastic polyps include juvenile, hyperplastic, inflammatory, and lymphoid polyps. Not all of these so-called nonneoplastic polyps may be innocent. There may be an increased risk of colorectal cancer in some families with multiple members affected with juvenile polyposis and hyperplastic polyposis.

See also: Colon cancer family history.