Colon polyps are clumps of cells that form in the lining of the large intestine or rectum. There are several types of polyps. Some of these polyps are benign, or noncancerous, while other types may become malignant over time. According to The American Society of Colon and Rectal Surgeons, all types of polyps can occur anywhere throughout the large intestine, but are most common in the sigmoid (left) colon and rectum.
Adenomatous polpys are the most common type of colon polyps, accounting for roughly two-thirds of all colon polyps, according to the Mayo Clinic. While not all adenomatous polyps will become cancerous, most polyps that are found to be malignant are of the adenomatous type. Adenomatous polyps may be classified as villous, tubular or tubulovillous according to their physical characteristics. According to eMedTV, villous adenomas are typically larger than other types and are also the most likely to become cancerous, while tubular adenomas are the least likely to become malignant.
According to Jackson Siegelbaum Gastroenterology, adenomatous polyps can be further subdivided according to their age of onset, disease course and pattern of presentation in the large intestine. Ordinary polyps tend to develop in people between the ages of 40 and 60 and are known to be genetically linked. Some ordinary polyps will eventually become cancerous, although it may take 10 years or more for them to become malignant. A genetic condition called hereditary familial polyposis causes the entire colon to be inundated with adenomatous polyps, sometimes starting as early as childhood. Most patients with this rare condition will develop cancer. Another hereditary condition called Lynch syndrome can cause numerous adenomatous polyps to develop throughout the colon. Common among close blood relatives, it can cause colon cancer to develop among people in their 20's to 40's.
Hyperplastic polyps make up the majority of the remainder of the colonic polyps along with adenomatous polyps. According to the Mayo Clinic, they occur most often in the sigmoid colon and rectum, although they can develop anywhere in the large intestine. They rarely become cancerous and are usually very small--less than 5 millimeters--in size.
Benign Colon Polyps
According to eMedTV, inflammatory and hamartomatous polyps can also develop in the sigmoid colon, rectum or other parts of the intestine; however, they are not known to cause cancer. Inflammatory polyps may develop among people with ulcerative colitis or Crohn's disease--inflammatory bowel disease that are characterized by chronic bouts of inflammation of the digestive tract, colon and/or rectum. The Mayo Clinic notes that these conditions do increase the risk of developing colon cancer, although the polyps themselves are not the underlying cause.