Somatostatinomas are rare, functional neuroendocrine tumors (NETs) that contain and produce excessive somatostatin, which inhibits numerous endocrine and exocrine secretory functions. A majority of somatostatinomas occur in the pancreas, although they may also occur in the duodenum and in more rare sites such as the jejunum, stomach, or biliary tract. The most common manifestations of somatostatinoma include abdominal pain and weight loss. However, presentation is variable based on tumor location, severity, and other factors. Somatostatinomas are often discovered during clinical investigation of possible NETs, and diagnosis involves detection of elevated somatostatin levels in tissue or plasma and by immunohistochemistry staining.
Quick Answers for Clinicians
Somatostatinoma syndrome is characterized by diabetes, gallstones, and diarrhea (usually steatorrhea). Somatostatinoma syndrome is thought to occur in less than 1% of patients with a somatostatinoma, and is more common in patients with pancreatic tumors than in those with intestinal tumors. The diagnosis of somatostatinoma syndrome can be established by measuring the plasma somatostatin level in patients who exhibit the characteristic symptoms.
Somatostatinomas may be associated with multiple endocrine neoplasia type 1 (MEN1), von Hippel-Lindau syndrome (VHL), neurofibromatosis type 1 (NF1), or polycythemia-paraganglioma-somatostatinoma syndrome. The National Comprehensive Cancer Network (NCCN) recommends that genetic testing for inherited syndromes be considered for all patients with pancreatic neuroendocrine tumors (PNETs) when appropriate, based on clinical suspicion.
Imaging is utilized for tumor localization and to determine disease severity. Common imaging methods for somatostatinomas include computed tomography (CT), magnetic resonance imaging (MRI), endoscopic ultrasound (EUS), somatostatin receptor scintigraphy (SRS), and positron emission tomography (PET).
Indications for Testing
Although somatostatinomas are often detected incidentally (eg, during clinical examination for abdominal pain, weight loss, or a suspected pancreatic tumor), laboratory testing is appropriate for patients who present with symptoms of somatostatin excess, including diabetes, gallstones, and diarrhea (usually steatorrhea).
Because of their low prevalence and variable presentation, somatostatinomas are rarely diagnosed before surgery or biopsy. Generally, somatostatinomas are discovered during exploratory laparotomy, radiography, or other imaging studies that are performed to investigate unexplained abdominal pain, weight loss, persistent diarrhea, diabetes, or other related conditions. As with other pancreatic neuroendocrine tumors (PNETs), serum chromogranin A measurements are recommended in the initial evaluation, and levels are expected to be elevated in cases of somatostatinoma. Once a tumor is detected, somatostatinomas are generally identified using plasma somatostatin measurements and immunohistochemistry staining.
The somatostatin level in plasma is commonly elevated in pancreatic somatostatinoma, whereas intestinal tumors will often present with normal or minimally elevated levels.
Immunohistochemical evaluation of tumor tissue is often valuable in the diagnosis of somatostatinoma. In many cases, stains such as somatostatin and chromogranin A are used to confirm diagnosis. For more information on immunohistochemistry tests, refer to ARUP’s Immunohistochemistry Stain Offerings.
ARUP Laboratory Tests
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NCCN - Neuroendocrine and Adrenal Tumors Version 1.2019
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Kulke MH, Anthony LB, Bushnell DL, et al. NANETS treatment guidelines: well-differentiated neuroendocrine tumors of the stomach and pancreas. Pancreas. 2010;39(6):735-752.
For additional immunohistochemistry test information, refer to ARUP Immunohistochemistry Stain Offerings