1. A 22-year-old man undergoes a distal pancreatectomy for a 6 cm mass in the tail of the pancreas. The tumor demonstrates a solid, gray to white-tan appearance with areas of hemorrhage and necrosis. Microscopically, the tumor is composed of small, round cells with scant cytoplasm arranged in nests and broad bands. The tumor also demonstrates nuclear immunolabeling for WT1 and diffuse labeling with antibodies to AE1/AE3. What is the most likely diagnosis?