Most bowel cancers are thought to develop from growths on the lining of the wall of the large bowel. These growths are called adenomas or polyps. Not all polyps develop into bowel cancer.
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.