Bowel polyps

Most bowel cancers start as benign, non-threatening growths – called polyps – on the wall or lining of the bowel.

Polyps typically grow in two shapes: flat or with a stalk. They can vary in size, ranging from a couple of millimeters to several centimetres.

Polyps are fairly common. Around 15-40% of adults have polyps. They are more common in men and older adults.

Polyps are usually harmless; however, adenomatous polyps can become cancerous (malignant) and if left undetected, can develop over time into a cancerous tumour.

The most common type of bowel cancer is called an adenocarcinoma, named after the gland cells in the lining of the bowel where the cancer first develops.

Other rarer types include squamous cell cancers (which start in the skin-like cells of the bowel lining), carcinoid tumours, sarcomas and lymphomas.

In advanced cases, the cancerous tumour can spread (metastasise) beyond the bowel to other organs.

 

Prevent, Detect and Diagnose

Bowel Cancer Australia’s resource explains the facts about bowel cancer, screening, high risk groups, symptoms you should be aware of.

Types of bowel polyps

Some polyps grow flat and project outward from a broad base. Others can be depressed, or project inward into the lining of the bowel. Doctors refer to these as sessile polyps.

Pedunculated polyps, on the other hand, may appear raised, projecting out into the hollow centre of the bowel. They may grow in the shape of a small cauliflower or mushroom suspended from a stalk or base.

Adenomas typically have three growth patterns: tubular, villous, and tubulovillous.

Tubular adenomas

Tubular adenomas are the most common type of bowel polyps, and usually account for 80% of all adenomatous polyps. Tubular adenomas are typically small pedunculated polyps, less than 1.2 centimetres in size. They usually have a tube-like or rounded shape. Tubular adenomas generally take years to form. Typically, the larger the polyp, the greater the risk it may become cancerous.

Villous adenomas

Villous adenomas are generally larger pedunculated polyps and grow in a cauliflower-like shape. The term ‘villous features’ refers to the finger-like or leaf-like projections. Villous adenomas are more likely to become cancerous. They account for 5-15% of all adenomatous polyps.

Tubulovillous adenomas

Tubulovillous adenomas contain a mixture of tubular and villous growth. They usually have 25-75% villous features, and they account for roughly 5-15% of all adenomatous polyps.

Serrated adenomas

Serrated adenomas contain tissues with a sawtooth look. There are two types: sessile serrated adenomas and traditional serrated adenomas. Most serrated adenomas are sessile and resemble small raised bumps. Sessile serrated polyps tend to carry a low risk of becoming cancerous as long as they do not contain major cellular changes. Traditional, or non-sessile, serrated adenomas are rarer and typically pedunculated. They carry a high risk of becoming cancerous.

Hyperplastic

Hyperplastic polyps are typically benign, and they are not usually a cause for concern. They will rarely become cancerous, as they have a low malignancy potential.

Inflammatory

Inflammatory polyps occur most often in people with inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis. Some people may also refer to these as pseudopolyps, as they are not true polyps but a reaction to inflammation in the colon. Inflammatory polyps are usually benign and generally do not carry the risk of developing into bowel cancer.