Colorectal cancer cell. Coloured scanning electron micrograph (SEM) of a culture of a Caco-2 adePhotographycarciPhotographyma cancer cell from the human colon showing apoptosis (programmed cell death). AdePhotographycarciPhotographymas of the colon and rectum make up 95 percent of all colorectal cancer cases. In the gastrointestinal tract, rectal and colon adePhotographycarciPhotographymas develop in the cells of the lining inside the large intestine. These adePhotographycarciPhotographymas typically start as a growth of tissue called a polyp. A particular type of polyp called an adePhotographyma may develop into cancer. Polyps are often removed during a routine coloPhotographyscopy before they may turn cancerous. 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. Magnification: x 4000 when printed 10 centimetres wide.