Colorectal cancer is the third leading cause of death from cancer in both males and females in Western society at present comprising 11% of all cancers. There is a nearly identical incidence in males and females, but a slight relative higher frequency of rectal cancer in males (in Western society).
The cancers of the colon and rectum will be considered together as many aspects of their occurrence, histopathological origin and behaviour are identical, although important differences in therapy will be highlighted. Colorectal cancer has an annual incidence in Western society of 500 per million of the population and deaths due to this disease are second only to lung cancer in men and breast cancer in women. By contrast the disease is relatively rare in Africa. Colon cancer is now 2.4 times as common as rectal cancer a change from 30 years ago when rectal cancer was relatively more common.
Rectal cancer is defined as a cancer that arises below the peritoneal reflection or more simply more than 12-15 cm from the anus.