1. A 38-year-old woman presents with abdominal pain and a palpable mass. Imaging reveals a well-defined, low-attenuation, multicystic mass in the tail of the pancreas. She undergoes a distal pancreatectomy. Microscopically, the tumor shows a gradual cystic transformation of the pancreatic parenchyma. The cysts are lined by one to several layers of cuboidal to low columnar cells with round, basally oriented nuclei and granular, eosinophilic apical cytoplasm. There is no significant nuclear atypia or mitotic activity. What is the most likely diagnosis?