Colorectal cancer. Artwork showing malignant (cancerous) tumours (red) in a patient's colon (large intestine) and rectum. Symptoms of colon cancer 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.