Colon polyps are growths that protrude from the surface of the colon. There are several types of colon polyps, including adenomatous polyps, hyperplastic polyps, and inflammatory polyps. Colon polyps are considered to be precursors to colon cancer and often are removed during colonoscopy.
Hyperplastic Polyps
Hyperplastic polyps, relatively small growths, tend to be less than 10mm in size. They often remain unchanged for a long time and do not cause colon cancer. Hyperplastic polyps are usually located in the lower section of the colon, according to the College of American Pathologists.
It is not always possible to determine which polyps are hyperplastic, based on appearance during colonoscopy. Therefore, hyperplastic polyps are often removed and biopsied to confirm they are not dangerous.
Adenomatous Polyps
Adenomatous polyps, or adenomas, are the precursors of 90 to 95 percent of colon cancer cases. In a 2004 study published in the "International Journal of Cancer," F. Loeve and colleagues reported that the evolution of cancer from adenomas may take five to 20 years.
As one gets older, the risk of developing adenomas increases. According to a 2007 study published in "Statistics in Medicine" by C.M. Rutter et al., roughly one-third of adults have one or more adenomas in the colon at 60 years old.
Adenomas are classified by their size, general appearance and specific features as seen under the microscope.
In general, the larger the adenoma is, the more likely it will become cancerous. Adenomas are also classified into tubular, villous and tubulovillous adenomas, according to their structure when viewed under a microscope. Villous adenomas are considered to be most dangerous, with a 30- to 70-percent chance of containing cancer cells, according to "Clinical Oncology."
Regular screening of the colon by colonoscopy can lead to removal of adenomas, hence stopping them from becoming cancer.
Inflammatory Polyps
Inflammatory polyps often occur after acute or chronic inflammation of the colon. Inflammatory polyps are associated with inflammatory diseases of the gastrointestinal tract, such as Crohn's disease and ischemic colitis, according to "Clinical Oncology." Inflammatory polyps are not at high risk of becoming cancer.
Hamartomatous Polyps
Hamartomatous polyps often occur at young ages and may cause rectal bleeding in children. Hamartomatous polyps are associated with hereditary syndromes, such as Peutz-Jegher or juvenile polyposis syndromes. Patients with Peutz-Jegher or juvenile polyposis syndromes might have up to 10 or more hamartomatous polyps in their colon at the time of diagnosis.
Hamartomatous polyps rarely lead to colon cancer. However, patients with Peutz-Jegher or juvenile polyposis syndrome are at a high risk of developing colon cancer at older ages, and their colons need to be screened regularly by colonoscopy.
References
- College of American Pathologists: Hyperplastic Polyp
- "Clinical Oncology"; Martin Abeloff et al., 2007
- "Statistics in Medicine"; A hierarchical non-homogenous Poisson model for meta-analysis of adenoma counts; Rutter et al., Jan. 15, 2007
