Scientists have discovered that large bowel cancer develops because of defects in the genes of cells lining the bowel. These cells start to multiply and form a small protrusion or 'polyp' on the bowel surface. The majority of polyps remain localised and cause no symptoms. However, further changes can occur in the cells within a polyp, which cause them to become cancerous. This is why removal of polyps can prevent cancer.
Cancer develops when cells begin to multiply at an abnormal rate.
Normally, cells die and are replaced in equal measure. When cells begin to multiply at a faster rate than they should, a growth forms of all the unwanted cells. This can go on to form a cancerous growth. The characteristics of cancer cells are that they invade the surrounding normal tissue and may spread to other organs. The reason for the altered behaviour of cells is linked to an abnormality in their genes.