Pancreatic neuroendocrine neoplasms: a current summary of diagnostic, prognostic, and differential diagnostic information.

Pancreatic endocrine tumors (PETs) continue to be challenging diagnostic and prognostic lesions in surgical pathology and clinical medicine. These neoplasms can be graded into 1 of 3 tiers, based on histologic characteristics in likeness to epithelial neuroendocrine tumors in other anatomic sites. However, grade 1 tumors are by far the most common and are the most difficult to prognosticate. The most helpful features by which to gauge the behavior of such lesions include size (3 cm or larger); mitotic activity (2 or more mitoses per 10 high-power [x400] microscopic fields); marked nuclear atypia, especially with atypical mitoticfigures; predominant tumor synthesis of gastrin, vasoactive intestinal polypeptide, somatostatin, glucagon, calcitonin, or adrenocorticotropic hormone; complete nonfunctionality of the tumor at an immunohistochemical level; or invasion of blood vessels, nerves, or adjacent organs by the neoplasm. Differential diagnosis of PETs includes lesions such as solid-pseudopapillary neoplasms, acinar carcinomas, metastatic neuroendocrine tumors, and plasmacytomas.