Ampullary carcinoma: Cancer of a structure called the ampulla of Vater, a small muscle located at the junction where the common bile duct (carrying bile from the liver and secretions from the pancreas) empties into the duodenum (upper small intestine).
Because of its location, this cancer can cause obstruction of the common bile duct and prevent bile from flowing into the intestine and out of the body. The chemicals usually eliminated from the body in bile -- in particular, bilirubin -- accumulate in the blood and cause jaundice (yellow skin and eyes) and itching. The stool becomes light-colored and the urine dark-colored since the accumulating bilirubin (which is yellow to dark brown) is eliminated in the urine instead of the stool.
The cause of ampullary carcinoma is unknown. Fortunately, it is rather rare.