Types of Colorectal Cancer

Precancerous conditions of the colon and rectum

Precancerous conditions have the potential to develop into cancer. The most common precancerous conditions of the colon and rectum are:

• adenomatous polyps (adenomas)
• polyposis syndromes
• familial adenomatous polyposis (FAP)
• hereditary non-polyposis colon cancer (HNPCC)

Adenomatous polyps - Adenomatous polyps (adenomas) have the potential to become cancer. It takes an average of 10 years for an adenomatous polyp to develop into an invasive colorectal cancer.The incidence of adenomas increases with age. More than 50% of people 80 years of age or older will have an adenoma. Most will develop in the rectum and sigmoid colon.

There are 3 types of adenomatous polyps:

• tubular adenomas

• look like a mushroom with a head and a stalk (pedunculated)
• the outer surface looks like a series of tubes
• can easily be removed during a colonoscopy
• are the most common and least likely of all adenomas to contain or develop cancer
• the larger the tubular adenoma, the greater the chance of it becoming malignant (polyps larger than 2 cm are more likely to develop into cancer)

• villous adenomas

• have a fuzzy appearance with numerous long, slender projections
• are usually flat with a wide, broad base (sessile)
• can become quite large, making them difficult to remove
• some of the colon may need to be surgically removed (resected) if the villous adenomas cannot be completely removed by polypectomy
• are the most likely to develop into cancer, especially if they are large

• tubulovillous adenomas

• appear to be a mixture of tubular and villous adenomas
• the likelihood of them becoming cancerous lies somewhere between the other 2 adenomas

Benign tumours of the colon and rectum

A benign tumour is a non-cancerous growth that does not spread (metastasize) to other parts of the body and is not usually life-threatening.

The most common benign tumours in the colon are colorectal polyps.

Benign colorectal polyps

About half of adults over the age of 40 develop lumps of tissue called polyps that grow from the inner lining (mucosa) of the colon or rectum. In most people, it is unclear how or why polyps develop. Polyps may look like a mushroom with a head and a stalk (pedunculated polyps). They may also be flat and grow along the inner surface of the wall of the colon or rectum (sessile polyps). Most polyps are non-cancerous (benign), but some do have the potential to become cancerous (malignant). Benign colorectal polyps are more common in men than women.

The most common type of benign polyp is hyperplastic polyp. Hyperplastic polyps are usually less than 0.5 cm in diameter and most commonly occur in the rectum and sigmoid colon.

There are several other types of benign polyps. The following benign polyps are much less common than hyperplastic polyps:

• inflammatory polyps (pseudopolyp)

• usually associated with chronic inflammatory bowel diseases such as Crohn′s disease or ulcerative colitis

• hamartomas

• contain normal cells that have an abnormal arrangement

• juvenile polyps

• also called retention polyps that contain many mucous glands
• usually occur as a single large polyp
• mostly found in children under 10 years of age

• lipomas

• develop within the fat cells in the colon

• lymphoid polyps

• contain lymphoid cells, a type of white blood cell