Rectal cancer. Coloured X-ray of the human abdomen in front view, showing the large intestine with cancer of the rectum. Bones of the skeleton are green. The large intestine (colon, purple) is at centre. At lower centre, the colon leads into the rectum (blue) which appears narrowed and mis- shapen due to cancer. The most common cancer of the rectum is adenocarcinoma, forming ulcer-like lesions which are associated with existing polyps (outgrowths of the rectal wall). Treatment usually involves surgery. This image was obtained when an opaque medium (like barium) was introduced into the intestine to make the gut visible on X-ray.