Polyps are growths (noncancerous, precancerous or cancerous) involving the lining of the bowel. They vary in size and can occur in several locations in the gastrointestinal tract but are most common in the colon. Some grow on a “stalk” and look like mushrooms, while some polyps are flat. Some polyps can contain small areas of cancer, although the vast majority of polyps do not.
Healthy cells grow and divide in an orderly way. Mutations in certain genes can cause cells to continue dividing even when new cells aren't needed. In the colon and rectum, this unregulated growth can cause polyps to form.
Polyps can develop anywhere in your large intestine. In general, the larger a polyp, the greater the likelihood of cancer.
Colon polyps usually do not cause symptoms unless they are larger than 1 cm (0.4 in.) or they are cancerous. The most common symptom is rectal bleeding. Sometimes the bleeding may not be obvious and may only be discovered after doing a screening test for blood in the stool called a fecal occult blood test (FOBT).
Colon polyps usually do not cause pain or a change in bowel habits unless they are large and are blocking part of the colon. These symptoms are rare, because polyps usually are discovered and removed before they become large enough to cause problems.
Unless colon polyps are large and cause bleeding or pain, the only way to know if you have polyps is to have one or more tests that explore the inside surface of your colon.
Several tests can be used to detect colon polyps. Two of these exams, flexible sigmoidoscopy and colonoscopy, also can be used to collect tissue samples (called a biopsy) or to remove colon polyps.
- Fecal occult blood test (FOBT). This is done to look for microscopic amounts of blood in stool. FOBT is a simple, low-cost screening tool for colon polyps or colon cancer. FOBT has been shown in studies to reduce the number of deaths from colon cancer. By itself, a positive FOBT is not evidence of colon polyps or colon cancer. And a negative FOBT (no blood found) does not mean that you do not have polyps or colorectal cancer. If a fecal occult blood test is positive for blood in the stool, it is important to have a colonoscopy to help your doctor find the source of the blood and remove polyps if they are found.
- Fecal immunochemical test (FIT). This test also looks for blood in the stool, but it is more specific than the FOBT. If the test is positive for blood in the stool, you may need to have a colonoscopy.
Tests that look inside your body:
- Flexible sigmoidoscopy. Flexible sigmoidoscopy allows the doctor to look at the lower third of the colon. During a sigmoidoscopy exam, samples of any growths can be collected (biopsied) and polyps can sometimes be removed.
- This screening method lets a doctor inspect the entire colon for polyps and cancer. During a colonoscopy, samples of any growths can be collected and polyps usually can be removed.
- Computed tomographic colonography (CTC). This test is also called virtual colonoscopy. A computer and X-rays make a detailed picture of the colon to help the doctor look for polyps. If this test finds polyps, you may need to have a colonoscopy to remove them.
If polyps found are hyperplastic, these are benign and cannot become cancerous. In this case you can continue your regular screenings.
Complications from colonoscopy are rare. There is a slight risk of:
- Puncturing the colon (less than 1 in 1,000) or causing severe bleeding by damaging the wall of the colon (less than 3 in 1,000).
- Bleeding caused by removing a polyp.
- Complications from sedatives given during the procedure.
If you have had one or more adenomatous polyps removed, you probably need regular follow-up colonoscopy exams every 3 to 5 years. Talk with your doctor about the follow-up schedule that he or she thinks is best for you.
Surgery is sometimes needed for large colon polyps that cannot be removed safely during a colonoscopy and may be more likely to develop into cancer.