Endocrine tumors account for less than 5% of all pancreatic tumors and are sometimes referred to as neuroendocrine or islet cell tumors. Islet cell tumors affect approximately 2500 people in the United States annually. Some of these tumors secrete excessive amounts of hormone and are referred to as functional neuroendocrine tumors. More common functional islet cell tumors include insulinomas and glucagonomas , whereas VIPomas, and somatostatinomas are much more unusual. Nonfunctional tumors are less common and do not secrete excess hormones.