Colorectal Polyps

What are colorectal polyps?

Colorectal polyps are growths that develop on the inner lining of the large bowel (colon or rectum). They are common — affecting approximately 15–40% of adults — and are more common with increasing age.

Most polyps are harmless. However, some types can gradually develop into bowel cancer if left untreated. While only a small percentage of polyps progress to cancer, nearly all bowel cancers begin as a polyp. The progression from a polyp to cancer is usually slow, occurring over 7–10 years.

Types of colorectal polyps

Polyps are described by both their appearance and microscopic features.

Subtypes based on appearance:

  • Flat

  • Sessile (broad-based)

  • Pedunculated (on a stalk)

  • Depressed

Microscopic subtypes:

1. Hyperplastic polyps

  • Small and commonly found in the rectum or sigmoid colon. Usually benign with minimal or no cancer risk

  • No surveillance required if found in isolation and under a certain size

2. Adenomatous polyps

  • The most common type of pre-cancerous polyp

  • Subtypes: tubular, tubulovillous, and villous adenomas (the latter two having higher risk in terms of cancer). The presence of abnormal cell changes known as high-grade dysplasia also increases the cancer risk

  • Surveillance colonoscopy is required and the time interval is based on the size, number, and microscopic features (i.e. presence of high grade dysplasia or villous changes)

3. Serrated precancerous polyps

  • Serrated polyps are a class of colon polyps that have a serrated or saw-toothed appearance under a microscope. Serrated polyps accounts for up to 25% of colorectal cancers. The subtypes of precancerous serrated polyps include sessile serrated lesions (SSLs) and traditional serrated adenomas (TSAs). SSLs are common while TSAs are rare

  • Often flat or subtle, typically found in the right colon and harder to detect, requiring experienced endoscopic assessment

  • Surveillance colonoscopy is necessary and the time interval is based on the size, number and microscopic features (i.e. presence of dysplasia)

4. Inflammatory Polyps

  • Seen in people with inflammatory bowel disease (IBD) such as Crohn’s disease or ulcerative colitis. These are usually non-cancerous and result from chronic inflammation. Although there is no malignant potential, patients generally still require surveillance colonoscopies given a higher bowel cancer risk based on their disease

What are the risk factors for precancerous polyps?

  • Age >50 years

  • Family history or personal history of polyps or colorectal cancer

  • Lifestyle factors:

    • Diet high in red or processed meats, low fibre intake, suboptimal diet quality, smoking, excessive alcohol, elevated body weight/obesity or a sedentary lifestyle

Do polyps increase the risk of bowel cancer?

Yes — certain polyps (i.e. adenomas and sessile serrated lesions) carry a risk of turning into colorectal cancer over time. Removal of such polyps significantly reduce a persons risk of bowel cancer

How are colorectal polyps treated?

Polyps are usually removed during colonoscopy. This is a safe and effective procedure performed by a gastroenterologist.

Treatment options include:

  • The mainstay of treatment is endoscopic removal (polypectomy), usually during colonoscopy. This is a safe and effective procedure. In some cases — for example, with larger or flatter lesions — more advanced techniques like endoscopic mucosal resection (EMR) may be used. In rare polyps with features suspicious for early cancer, a technique called endoscopic submucosal dissection (ESD) is required

  • Surgery is required if there is evidence of cancer within a polyp that has invaded deeper layers (known as submucosal invasion) or the polyp cannot be safely removed endoscopically

What is the surveillance after a polyp is removed?

After removal of a pre-cancerous polyp, follow-up colonoscopy is recommended. The timing depends on:

  • Number of polyps

  • Size

  • Type (histology)

  • Presence of high-grade dysplasia

Surveillance intervals typically range from 6 months to 10 years