Stomach cancer. Coloured frontal X-ray of the upper gastroduodenal tract of a patient with stomach cancer (grey, upper centre). The gastrodudenal tract is where the stomach joins the duodenum (white, lower centre), the first stage of the small intestine. Sections of the gut show up as white because a radio-opaque barium meal was given prior to the X-ray. This highlights the structure of the gut. Any narrowing or obstructions, such as the cancer shown here, prevent the passage of the barium meal. They therefore do not show as white, allowing their location to be pinpointed.