Colorectal cancer

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Adenomas, or adenomatous polyps, are abnormal growths attached to the lining of the colon or rectum. They are a precancerous condition that can develop into cancer if left untreated.

Adenomas are usually polypoid, which means that they stick out from the lining and grow toward the hollow centre of the colon or rectum. They are also usually pedunculated, which means they are the shape of mushrooms with a stem, or stalk. If they look like mushroom caps without the stem, they are described as sessile. Sometimes adenomas lie very flat against the lining of the colon or rectum. They can also have jagged, or serrated, edges like a saw.

Types of adenomas

There are 3 types of adenomas. Each type is described based on the growth pattern of cells in the adenoma, which is how the cells look when viewed under a microscope.

Tubular adenomas are the most common type. The cells in these adenomas look like tubes.

Villous adenomas have cells with finger-like projections. They are often larger than tubular adenomas.

Tubulovillous adenomas have cells with both tubular and villous growth patterns.

Adenomas with cells that have a villous growth pattern have the greatest risk of developing into cancer. This means that villous adenomas and tubulovillous adenomas are more likely to become cancer than tubular adenomas.

Adenomas are usually less than 1 cm in size. Adenomas larger than 1 cm also have a greater risk of developing into cancer.

Dysplasia can be found in adenomas. Dysplasia describes changes to cells that line the colon or rectum. When seen under a microscope, dysplastic cells look different from normal cells.

There are different levels of dysplasia. Mild, or low-grade, dysplasia means the cells are slightly abnormal. Severe, or high-grade, dysplasia means the cells look very abnormal and most like cancer cells.

Risk factors

The following risk factors have been linked to increasing your chance of developing adenomas:

  • being 50 years of age or older
  • family history of polyps or colorectal cancer
  • hereditary syndromes like familial adenomatous polyposis (FAP)
  • eating a diet high in fat and low in fibre
  • physical inactivity
  • being overweight


Most adenomas do not cause any symptoms. If symptoms develop, they can include:

  • changes in bowel habits, such as mucus in the stool
  • bleeding from the rectum
  • anemia
  • fatigue


If you have symptoms or your doctor thinks you might have adenomas, you will be sent for tests. Tests used to diagnose adenomas may include:

  • digital rectal exam (DRE)
  • colonoscopy
  • virtual colonoscopy (also called CT colonography)
  • flexible sigmoidoscopy
  • barium enema
  • biopsy (usually done during a colonoscopy or flexible sigmoidoscopy)

Find out more about these tests and procedures.

Treatment and follow-up

The most common treatment for an adenoma is to remove it (called polypectomy) during colonoscopy or sigmoidoscopy. Depending on the number and type of adenomas, the amount of dysplasia and how severe the dysplasia is, doctors may do a bowel resection. Your doctor may suggest you have regular follow-up with a colonoscopy or sigmoidoscopy to check for more adenomas.

familial adenomatous polyposis (FAP)

An inherited condition that causes hundreds to thousands of polyps to develop, mainly on the lining of the colon and rectum.

People with FAP have a higher risk of colorectal cancer and small intestine cancer. It also increases the risk of stomach, adrenal gland and thyroid cancers.


Dr Darren Brenner The impact of lifestyle and the environment on cancer

Great progress has been made

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Some cancers, such as thyroid and testicular, have survival rates of over 90%. Other cancers, such as pancreatic, brain and esophageal, continue to have very low survival rates.

Learn more