NCI: A usually slow-growing epithelial neoplasm with ductal differentiation that arises from the exocrine pancreas and grows mostly within the pancreatic ducts. Grossly, it is characterized by the presence of intraductal masses. Morphologically, there is proliferation of mucin-producing cells within the pancreatic ducts, intraductal accumulation of mucin, and a papillary growth pattern. It may be associated with the presence of an invasive carcinoma. It usually occurs in older patients. Signs and symptoms include epigastric pain, weight loss, jaundice, chronic pancreatitis, and diabetes mellitus.