Bowel Cancer

Introduction
Bowel Cancer or Colorectal Cancer, a growth of malignant cells affecting, initially, the colon or rectum of the large intestine. Cancer starts when a bowel cell suffers alterations to its DNA (see Nucleic Acids), which cause it to abandon the normal controls on cell growth. The cells continue to proliferate until they form a polyp (a small tumour of the mucous membrane). Most polyps in other parts of the body are benign, but some occurring in the bowel may become cancerous.

SYMPTOMS
A change in bowel habit (especially constipation) is the most notable symptom, but watery diarrhoea is also possible. Rectal bleeding; pain; and tenesmus (a constant feeling of incomplete emptying of the rectum) are also possible symptoms.

DIAGNOSIS AND SCREENING
Bowel cancer is 90 per cent curable when diagnosed early and can be prevented by removing precancerous polyps. Unfortunately, most cases in the United Kingdom are not discovered early enough for a cure. Therefore, a suitable screening test has the potential to save many lives. The overall survival rate for bowel cancer in England and Wales is about 40 per cent.

One method is a test for blood in the stool called Haemoccult. However, it is not totally accurate, as it is only capable of finding 60 per cent of bowel cancers and 20 per cent of precancerous polyps. Researchers are investigating more accurate tests that detect DNA mutations in cells shed by the bowel lining into the stool.

Another way of screening uses a sigmoidoscope, an instrument that is inserted into the rectum to examine that part of the bowel and the sigmoid colon. Sigmoidoscopy usually finds benign polyps, and removing these growths almost halves a person’s cancer risk for ten years. A recent study showed that a once-only screening between the ages of 55 and 64 might prevent 5,500 cancers annually and 3,500 deaths in Britain. A large study is under way to evaluate this approach.

TREATMENT
The main treatment is surgery—removal of the tumour and, often, part of the bowel followed by resection. Nothing further is necessary provided the cancer has not spread beyond the bowel wall. Unfortunately, the prognosis is less favourable once the cancer has spread, as metastases tend to be resistant to chemotherapy and radiotherapy. However, there are numerous trials aimed at remedying this situation.