Autoimmune pancreatitis with response to chemoradiation therapy

Autoimmune pancreatitis (AIP) sometimes mimics pancreatic cancer, and is rarely resected under this misdiagnosis. However, there is no report in the literature regarding a case of AIP, which was misdiagnosed as an inoperative stage of pancreatic cancer and which received systemic chemotherapy with or without radiation. We report a 59-year-old man with a mass-forming lesion at the pancreatic head involving the common hepatic artery and portal vein, initially diagnosed as locally advanced pancreatic cancer and treated with chemoradiation therapy. After a month of continuous infusion of low dose 5-fluorouracil with concurrent local radiation (50.4 Gy), the pancreatic lesion diminished in size. However, the pancreatic body gradually enlarged and a capsule-like limb appeared in the following year. Serological markers and endoscopic retrograde cholangiopancreatography were compatible with those of AIP. No neoplastic tissue was identified on the fine needle aspiration biopsy of the pancreas. The pancreatic lesion responded well to steroid therapy and the patient remained in remission for one year after the withdrawal of steroids. Similar to pancreatic cancer, this current case of AIP responded to chemoradiation. Both serological and histological examinations were essential for images equivocal for either locally advanced pancreatic cancer or AIP.