Cancer of the colon. Coloured X-ray showing cancer of the large intestine, or colon. The colon occu- pies the right-hand part of the image, coloured red. At the bottom is the rectum (white). The constriction at centre right is caused by a tumour that has grown in the colon's wall, narrowing the internal cavity. The dark blue structures behind the colon and rectum are the bones of the spine and pelvis. The large intestine was highlighted on this image by giving the patient a barium enema before taking an X-ray. The barium coats the intestine's inside wall and shows up strongly on the X-ray film.