Both cancerous and noncancerous tumors of the bile duct or gallbladder are rare. When cancerous, these tumors are almost always fatal. The exception is a cancerous tumor of the gallbladder that is discovered accidentally, such as during gallstone removal surgery. If discovered in this way, the tumor may have been caught early enough to be removed completely, possibly producing a cure. When cancer of the gallbladder is diagnosed, there is almost always a co-existing medical condition found at the same time. Which of the following is the most likely associated medical condition?