VIPomas are rare neuroendocrine tumors that secrete vasoactive intestinal polypeptide (VIP). They are detected in 1 in 10 million people per year . The majority of VIPomas arise within the pancreas, and are classified as a pancreatic neuroendocrine (islet cell) tumor along with insulinoma, glucagonoma, somatostatinoma, and gastrinoma. However, other VIP-secreting tumors have been reported, including bronchogenic carcinoma, colon carcinoma, ganglioneuroblastoma, pheochromocytoma, hepatoma, and adrenal tumors. In children, VIPomas occur in sympathetic ganglia and in the adrenal glands . (See "Classification, epidemiology, clinical presentation, localization, and staging of pancreatic neuroendocrine tumors (islet-cell tumors)", section on 'Classification and nomenclature'.)
Symptomatic pancreatic VIPomas are usually solitary, more than 3 cm in diameter, and occur in the tail of pancreas in 75 percent of patients. Approximately 60 to 80 percent of VIPomas have metastasized by the time of diagnosis [2,3].
VIPomas usually occur as isolated tumors, but are part of the multiple endocrine neoplasia syndrome type 1 (MEN1) in 5 percent of patients. The latter patients may also have primary hyperparathyroidism, pituitary tumors, gastrinoma, and other tumors. (See "Multiple endocrine neoplasia type 1: Clinical manifestations and diagnosis".) In one report of 580 patients with the MEN-1 syndrome, only 2 (0.65 percent) harbored a VIPoma .
Vasoactive intestinal polypeptide (VIP)is a 28 amino acid polypeptide that binds to high affinity receptors on intestinal epithelial cells, leading to activation of cellular adenylate cyclase and cAMP production. This results in net fluid and electrolyte secretion into the lumen [5,6]. VIP also has other actions that may be clinically important in patients with a VIPoma (table 1). (See "Vasoactive intestinal polypeptide".)
The VIPoma syndrome is caused by excessive, unregulated secretion of VIP by the tumor. However, other substances, such as prostaglandin E2, may occasionally be secreted by the tumors . Analysis of a primary VIPoma tumor identified defects in the mismatch repair gene MSH2, as well as overexpression of the chemokine CXCR4 present in hepatic metastases .