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There are a number of different names for bowel cancer, which can be confusing. Bowel cancer is the most usual name for the disease in the colon or rectum (together called the large bowel).
Cancer that begins in the colon is called colon cancer. Cancer that begins in the rectum is called rectal cancer. The medical name for cancers affecting either of these parts of the body is colorectal cancer. (Sometimes this cancer is called large bowel cancer or cancer of the large intestine.)
The two cancers are named together because they are similar in the way they behave, in their causes, and in their treatment.
Cancer of the small bowel (the small intestine - made up of the duodenum, the jejunum and the ileum) and cancer of the anus are not included in the term.
Nearly all bowel cancer develops in the large bowel.
The colon and rectum are parts of the body's digestive waste system. The colon removes large amounts of water from any remaining undigested food which has passed through the stomach and small intestine. The rectum then stores the solid waste (faeces) until it passes out of the body through the anus (back passage).
Bowel cancer occurs when normal body cells in the lining of the large bowel get out of control, multiply and spread. When cancer starts like this, in the lining of an organ like the large intestine, it is called a carcinoma. Other types of colon cancer are rare and include lymphoma, carcinoid tumours, melanoma and sarcomas, and they are not discussed here.
Most bowel cancers develop from pre-cancerous growths known as polyps (sometimes called 'adenomas'). These are cells that form a lump, some of which become a cancerous (malignant) tumour. The tumour then grows and damages healthy parts of the body.
