Colon cancer. Coloured barium X-ray showing cancer of the human colon (large intestine). The cancerous region is the pointed dimpled structure at upper left. Opaque to X-rays, barium is given rectally (barium enema) to examine the rectum and colon. The barium coats the intestine's inside wall and shows up strongly on the X-ray film. The colon is one of the most common cancer sites. Treatment in most cases is by a partial colectomy (removal of part of the colon). Over 50 percent of patients survive five years after a colectomy. Also seen in the background are the pelvic bones at lower frame.