Pancreatic Doppelgängers: A Case of Misdiagnosed Identity.

IgG-4 related disease (IgG4-RD) is an autoimmune disease that can affect multiple organs and mimic adenocarcinoma of the pancreas. We describe the case of a 74-year-old man who presented with pancreatic mass and biliary obstruction. He was initially diagnosed with pancreatic adenocarcinoma and was started on chemotherapy. Eventually, he was diagnosed with IgG-4 related disease with autoimmune pancreatitis type 1 and IgG-4 sclerosing cholangitis with rapid improvement of symptoms and clinical findings after receiving steroid therapy.