PPoma and Nonfunctioning Neuroendocrine Tumor

PPomas secrete pancreatic polypeptide, but this hormone does not appear to cause symptoms in men and this tumor is considered nonfunctional. PPomas and nonfunctioning pancreatic neuroendocrine tumors are tumors that have no functional syndrome. Dopamine agonists have been shown to decrease circulating levels of PP and chromogranin A in patients with large unresectable islet cell tumors.75 PPomas produce symptoms by tumor mass effects. This tumor is diagnosed because the patient has cachexia, abdominal pain, intestinal bleeding, blockage, or hepatomegaly. Patients with these tumors have also presented with clinical signs and symptoms of pancreatitis.76,77 Patients commonly have locally advanced or metastatic neuroendocrine tumor by the time of diagnosis.

Nonfunctioning pancreatic neuroendocrine tumors or PPomas usually cannot be differentiated from other malignant tumors of the pancreas before biopsy. Preliminary studies suggested that plasma marker 7B2 may be a good indicator of nonfunctional pancreatic neuroendocrine tumors.78 However, this has not been the case, and serum levels of chromogranin A or PP have been the best markers. Tumors can be found incidentally during any operative procedure.79 Patients with a long survival (>5 years) and with suspected metastatic pancreatic adenocarcinoma may have a nonfunctioning neuroendocrine tumor or PPoma rather than an exocrine carcinoma. Typically, these tumors are large when diagnosed (>5 cm), and almost all are malignant (70% to 92%).80 Nonfunctioning pancreatic endocrine tumors are differentiated from PPomas on the basis of results of the serum PP assay. At present, there are no data that suggest that PPomas or nonfunctioning pancreatic endocrine tumors differ in biologic behavior from malignant functioning neuroendocrine tumors.8182 However, recognizing that a tumor is a PPoma may be clinically important in that serum

PP levels may be used to monitor the results of antitumor therapies such as surgical resection or chemotherapy.

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