1. A 65-year-old man undergoes a pancreatoduodenectomy for a 5 cm mass in the head of the pancreas. Grossly, the mass is well-demarcated, soft, and gelatinous. Microscopically, the tumor is composed of large pools of extracellular mucin embedded in connective tissue stroma. There are clusters and strips of neoplastic cells suspended in the mucin, with prominent intracellular mucin. What is the most likely diagnosis?