The bowel forms part of the digestive system. The digestive system, or alimentary canal, is the path that food follows through your body. Leaving the mouth, food enters the oesophagus and travels down to the stomach. The food in the stomach empties into the small intestine, or small bowel, and the food passes then to the large intestine. The large intestine is also known as the large bowel, and is divided into two parts: the colon and the rectum. The colon makes up most of the 1.5 metre length of the large bowel. The colon is responsible for absorbing water, vitamins and minerals from the intestinal contents and conserving them. The rectum is the last part of the bowel, and its function is to form stools, and rid the body of undigested material.
Cancers of the small bowel are very rare. Colon and rectum cancers are much more common and so 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 polyps. Polyps are finger-like growths from the wall of the intestine that protrude into the intestinal cavity. These benign polyps are not cancer and relatively common in people over age 50. Polyps can become cancerous though, and the cancer may invade the normal bowel and spread to other parts of the body (). The 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.