1. A 60-year-old woman presents with abdominal pain and jaundice. She undergoes a pancreatoduodenectomy for a 5 cm mass in the head of the pancreas. Microscopically, the tumor is composed of spindle cells with a variably dense, “patternless” growth pattern, with variable amounts of collagen. There is a prominent branching, hemangiopericytoma-like vascular pattern. What is the most likely diagnosis?