The bowel forms part of the digestive system. It is divided into two parts, the small bowel and the large bowel. The large bowel is made up of the colon and rectum. The colon makes up most of the 1.5 metre length of the large bowel. In the path that food follows through your body, the alimentary canal, the colon follows the oesophagus, stomach and small bowel and comes before the rectum. The colon is responsible for absorbing water, vitamins, and minerals from the intestinal contents and conserving them. It also mixes the intestinal contents, forms stools, and rids the body of undigested material.

Colon and rectum cancers are sometimes referred to together as "bowel cancer". Bowel cancer is the second most common cancer in Australia after skin cancer. Each year, there are over 7000 new cases of bowel cancer in men and over 6000 cases in women. Most cases of bowel cancer begin with the development of benign polyps, finger-like growths that protrude into the intestinal cavity. These benign polyps are not cancer and relatively common in people over age 50. They can become cancerous though, with the ability to invade the normal bowel and spread to other parts of the body (metastasise). The tumours can create blockages in the intestine, preventing elimination.

The exact causes of bowel cancer are not known, but risk appears to be associated with genetic, dietary, and lifestyle factors. Those with a personal or family history of bowel cancer or polyps are at a higher risk, as are those with ulcerative colitis, inflammatory bowel disease, and immunodeficiency disorders. A very rare inherited disease, called familial adenomatosis or polyposis, causes benign polyps to develop early in life and cancer develops in almost all affected persons unless the colon is removed. Risk increases with age and with the occurrence of cancers in other parts of the body. High fat and meat diets are risk factors, especially when combined with minimal fruit, vegetable, and fibre intake. Lifestyle factors include cigarette smoking, obesity, and a sedentary lifestyle.