Abstract
An 80-year-old man was admitted due to biliary stricture with autoimmune pancreatitis. Although radiographical examinations suggested Immunoglobulin G4-related sclerosing cholangitis (IgG4-SC), punched biopsies from the bile duct revealed adenocarcinoma. In the resected specimen, abundant N-terminus of Forkhead box P3 (Foxp3)-positive cells were localized in cholangiocarcinoma (CCA) tissue, while IgG4-positive cells were spread around the entire bile duct. Therefore, the case was diagnosed with IgG4-SC accompanied by CCA, not sporadic CCA. We herein report an informative case wherein IgG4-positive cells were abundant in CCA tissue and Foxp3 immunohistochemical staining allowed us to determine that this case had two entities.