Colon cancer. Barium enema X-ray of the abdomen of a patient with cancer of the caecum, a part of the colon. The barium (bright areas) has filled this part of the colon, except for a dark area (centre) that is the cancer. The caecum, the first part of the colon, is in the right lower quadrant of the abdomen. The colon (or large intestine) then runs around the abdomen, forming one of the final parts of the digestive tract. Colon cancer is one of the most common cancers in North America and Western Europe. It is thought to be connected to a high fat and low fibre diet. Treatment depends upon the extent of the cancer. Barium, opaque to X-rays, is given as an enema to image the colon and rectum.