Pancreatic Endocrine Neoplasms

Pancreatic endocrine neoplasms (PENs) are foregut endocrine tumors that arise in the pancreas and appear morphologically similar to other neuroendocrine (carcinoid) tumors throughout the body. However, the biology of endocrine/neuroendocrine tumors tends to depend upon the site of origin. PENs can produce various hormones, though most are nonfunctional. They are generally low grade, well-differentiated tumors. PENs can be classified according to grade, size, or functional status. The nomenclature of these neoplasms can be confusing, partly because of the variable terminology, including different names for the same neoplasm (including “islet cell tumors,” “pancreatic neuroendocrine tumor,” and “pancreatic endocrine tumors”) and partly because well-differentiated malignant tumors can either be called “malignant pancreatic endocrine neoplasms” or “pancreatic endocrine carcinomas.” The authors of the AFIP fascicle prefer to consider all well-differentiated PENs as potentially malignant (with the exception of micro­adenomas less than 0.5 cm in size). The term “carcinoma” is reserved for poorly differentiated lesions. Similarly, the term PEN will be used in this chapter to refer to well-differentiated tumors.