A colon polyp is a small clump of cells that forms on the inner lining of the colon or rectum. Most polyps are harmless, but over time some can turn into colorectal cancer. Almost all colorectal cancers begin from a polyp, although only a small proportion of polyps ever become cancerous, and the process usually takes many years. In general, the larger a precancerous polyp, the greater the risk that it will eventually become cancer.
Because polyps rarely cause symptoms but can be removed before they become dangerous, detecting and removing them through screening is one of the most effective ways to prevent colorectal cancer.
Polyps are broadly divided into those that are precancerous and those that are generally harmless.
Precancerous (neoplastic) polyps:
- Adenomas (adenomatous polyps), the most common precancerous type, which include tubular adenomas (most common, lowest risk), tubulovillous adenomas (higher risk), and villous adenomas (least common but most likely to become cancerous, especially when large)
- Sessile serrated lesions, which are flat, often in the right side of the colon, harder to detect, and can progress to cancer
- Traditional serrated adenomas, which are rare but clearly precancerous and are always removed
Generally harmless (non-neoplastic) polyps:
- Hyperplastic polyps, which are very common, usually small, and almost never become cancer
- Inflammatory polyps, associated with inflammatory bowel disease; the polyps themselves do not become cancer, but they signal chronic inflammation that raises overall risk
- Hamartomatous polyps, usually harmless when single
Symptoms
Most people with colon polyps have no symptoms, and polyps are usually found during routine screening. When symptoms do occur, they may include:
- Rectal bleeding
- Blood in the stool, seen as red streaks or black stool
- A change in bowel habits, such as constipation or diarrhea lasting longer than a week
- Iron-deficiency anemia from slow, chronic bleeding, which can cause fatigue and weakness
- Cramping or abdominal pain, if a large polyp partly blocks the bowel
Treatment
The standard treatment is removal of the polyp (polypectomy) during colonoscopy. Larger or more complex polyps may require endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD).
Every removed polyp is examined under the microscope, and the results determine when the next colonoscopy should be. The interval depends on the number, size and type of polyps found. As examples, based on current guidelines after a high-quality colonoscopy with complete removal:
- A normal exam with no adenomas, or one to two small tubular adenomas, generally leads to a longer interval before the next colonoscopy
- Larger or more numerous polyps, or those with higher-risk features, lead to shorter surveillance intervals
Your doctor will set the exact timing based on your individual results.
Causes and Risk Factors
Polyps form when the normal growth and repair of cells in the colon lining goes off track, usually due to genetic changes. Most polyps occur randomly, but several factors increase the risk:
- Age, with most people who have polyps being 45 or older
- A family history of advanced polyps or colorectal cancer
- A personal history of colon polyps
- Inflammatory bowel disease, such as ulcerative colitis or Crohn’s disease
- A diet high in fat and low in fibre, and high intake of red and processed meat
- Obesity and lack of exercise
- Smoking and heavy alcohol use
- Type 2 diabetes
Some inherited syndromes greatly increase the risk, including Lynch syndrome, which is the most common inherited form, and familial adenomatous polyposis (FAP), which causes very large numbers of polyps and, if untreated, an extremely high risk of colon cancer at a young age.
Diagnosis and Detection
Colonoscopy is the gold standard, because it both finds polyps and allows them to be removed and examined during the same procedure. Other detection tests include CT colonography, flexible sigmoidoscopy, and stool tests such as the faecal immunochemical test (FIT) and multi-target stool DNA tests. Any positive result from a non-colonoscopy test should be followed by a colonoscopy.
Current guidance in the United States recommends that people at average risk begin regular colorectal cancer screening at age 45, continuing to around age 75 for those in good health, with decisions between ages 76 and 85 made individually. People at higher risk may need to start earlier and be screened more often. Screening intervals depend on the test used, for example colonoscopy every 10 years for those at average risk with a normal result.
Prevention and the Importance of Screening
Removing polyps helps prevent colorectal cancer, and regular screening is considered the best form of prevention. Lifestyle measures that may lower risk include a diet rich in fruit, vegetables, whole grains and fibre, reduced fat, limiting alcohol, not smoking, regular physical activity, and maintaining a healthy weight.
When to See a Doctor
See a doctor if you have abdominal pain, blood in the stool, a change in bowel habits lasting longer than a week, or unintended weight loss. Make sure to keep up with regular screening if you are 45 or older, or younger than 45 if you have conditions or a family history that raise your risk of colorectal cancer.