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Colorectal (Bowel) Cancer

Colorectal cancer is a malignant (cancerous) growth that develops most commonly inside the large bowel. Cancer of the large bowel is also known as colorectal cancer.

The bowel is part of the food digestive system. It connects the stomach to the anus, where waste materials (called a bowel motion or faeces) are passed out of the body. The function of the bowel is to finish digesting food by absorbing water and nutrients.

The bowel has three main parts:
  • the small bowel, which mainly absorbs nutrients from broken-down food
  • the colon, which mainly absorbs water
  • the rectum, which stores waste material until it is passed from the body through the anus.

The colon and rectum together are known as the large bowel. Bowel cancer usually affects the large bowel. Cancer of the small bowel is rare.

Most bowel cancers develop from tiny growths inside the colon or rectum called polyps, which look like small spots on the bowel lining. These polyps are usually harmless (benign) but some can become cancerous (malignant) and spread. If polyps are removed, the risk of bowel cancer is reduced.

Bowel cancer spreads (metastasises) outside the bowel if it is not treated. It spreads fairly slowly and can stay in the bowel for months or years before moving outside it, first to the lymph nodes, then to other organs such as the liver or lungs.


Possible signs of bowel cancer include the following:

  • a change in normal bowel habits
  • pain in your abdomen or rectum
  • unexplained weight loss
  • bleeding from your rectum or blood in your stools
  • a straining feeling in your rectum