Colon cancer. Coloured scanning electron micrograph (SEM) of cancer cells from the human colon (large intestine). Cancerous (malignant) cells divide rapidly and uncontrollably and are able to invade and destroy surrounding tissue. Cancer of the colon is also known as colorectal cancer. Symptoms include rectal bleeding and abdominal pain. Treatment is with surgery to remove the affected area. Colon cancer is one of the most common cancers in the Western world. It is a disease of late and middle age. Risk factors include a diet high in animal fat and low in fibre and a sedentary lifestyle.