1. A 65-year-old man presents with intermittent abdominal pain and weight loss. An endoscopic retrograde cholangiopancreatography (ERCP) shows a dilated main pancreatic duct without a stricture. There are filling defects in the duct that are caused by papillary projections. The patient undergoes a pancreatoduodenectomy. What is the most likely histologic type of intraductal neoplasm?