1. A 55-year-old man presents with abdominal pain and a palpable mass. He undergoes a distal pancreatectomy. The tumor is well-circumscribed, soft, and fleshy. The mass shows a characteristic "zellballen" pattern with nests of uniform, polygonal cells with basophilic cytoplasm. There is a thin fibrous pseudocapsule. What is the most likely diagnosis?