Update on pancreatic endocrine tumors.

Endocrine tumors of the pancreas represent 1% to 2% of all pancreatic neoplasms. The tumors tend to have an indolent behavior, and long-term survival is common. There is no gender or age predilection. Patients can present with symptoms due to hormonal excess or a local mass effect or be asymptomatic. The tumors tend to be solid and well circumscribed. Typical microscopic findings include an organoid pattern of growth, with cells containing scant to moderate amounts of cytoplasm, and nuclei with dispersed chromatin and inconspicuous nucleoli. The morphologic spectrum of these tumors can be variable, and the differential diagnosis includes chronic pancreatitis with neuroendocrine hyperplasia, ductal adenocarcinoma, solid pseudopapillary tumor, acinar cell carcinoma, and pancreatoblastoma. The classification of these tumors remains controversial, and prognosis is difficult to predict, but important features include metastasis and invasion of adjacent structures. Resection remains the mainstay of surgical treatment. It is important to be aware that unusual morphologic variants of pancreatic endocrine tumors are common, and immunohistochemical stains can help avoid misdiagnosis.