Somatostatinoma

Diagnosis

Indications for Testing

  • Neuroendocrine symptoms compatible with specific tumor; presence of pancreatic tumor with neuroendocrine symptoms

Laboratory Testing

  • Somatostatin level – usually elevated many-fold above normal
    • Intestinal somatostatinomas may have normal or only slightly increased levels
  • Provocative tests are available with infusion tolbutamide and arginine

Histology

  • Nested or trabecular arrangement of small- to medium-sized cells
    • Unique occurrence of psammoma bodies
    • Finely granular eosinophilic cytoplasm
    • Central round to oval nuclei
    • Stippled chromatin (“salt and pepper”)
    • Typically >5cm
  • Immunohistochemistry – synaptophysin, chromogranin A, Ki-67, NSE, PGP 9.5
    • Tumor-specific confirmation – somatostatin with diffuse immunoreactivity

Imaging Studies

  • CT/MRI/endoscopic ultrasound
  • Somatostatin-receptor scintigraphy

Differential Diagnosis

Clinical Background

Somatostatinomas are rare, functional neuroendocrine tumors that produce excessive amounts of somatostatin. They occur in the pancreas and duodenum.

Epidemiology

  • Incidence – <1/1,000,000 (~10% of functioning PNETs)
  • Age – median is 40s
  • Sex – M<F, 1:2
  • Occurrence – usually sporadic

Risk Factors

  • Genetic
    • May also be associated with von Hippel-Lindau syndrome, tuberous sclerosis, and neurofibromatosis type 1 (von Recklinghausen disease)

Pathophysiology

  • Locations for tumor – duodenum (40%) or pancreas (60%)
  • Hormone secretion is somatostatin
    • Inhibits the release of many hormones (gut hormones, including insulin, pancreatic polypeptide, glucagon, gastrin, secretin, glucose-dependent insulinotropic peptide, and motilin; growth hormone)
    • Neurotransmitter function
  • Significant number of these tumors are metastatic

Clinical Presentation

  • Somatostatinoma syndrome
  • Tumor may be found incidentally if not associated with the syndrome (patient will be asymptomatic)
  • Metastatic disease is frequently found at the time of diagnosis
    • 80% of pancreatic and 50% of intestinal tumors are metastatic at presentation

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Somatostatin Quantitative, Plasma 2010001
Method: Quantitative Extraction/Immunoassay

Aid in diagnosis of somatostatinoma

Modest somatostatin elevation may also occur in nonendocrine disorders

Serial fasting somatostatin levels should be obtained at 3 months and then at 6-month intervals after surgical resection

Synaptophysin by Immunohistochemistry 2004139
Method: Immunohistochemistry

Aid in histologic identification of neuroendocrine tissue

Stained and returned to client pathologist for interpretation; consultation available if needed

   
Chromogranin A by Immunohistochemistry 2003830
Method: Immunohistochemistry

Aid in histologic identification of neuroendocrine tissue

Stained and returned to client pathologist for interpretation; consultation available if needed

   
Pan Cytokeratin (AE1,3) by Immunohistochemistry 2003433
Method: Immunohistochemistry

Aid in histologic diagnosis of somatostatinoma

Stained and returned to client pathologist for interpretation; consultation available if needed

   
Ki-67 with Interpretation by Immunohistochemistry 2007182
Method: Immunohistochemistry

Aid in determining NET grade

Determine mitotic rate in tissue

Stained and resulted by ARUP

   
Neuron Specific Enolase, Polyclonal (NSE P) by Immunohistochemistry 2004052
Method: Immunohistochemistry

Aid in histologic identification of neural and  neuroendocrine tissue

Stained and returned to client pathologist for interpretation; consultation available if needed

   
Protein Gene Product (PGP) 9.5 by Immunohistochemistry 2004091
Method: Immunohistochemistry

Aid in histologic diagnosis of somatostatinoma

Stained and returned to client pathologist for interpretation; consultation available if needed