Somatostatinoma

Diagnosis

Indications for Testing

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

Laboratory Testing

• Somatostatin level – ≥160 pg/mL
  • On average, a patient with pancreatic somatostatinoma has levels >50-fold over the reference range
  • 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

• Diabetes mellitus (type 1 or 2)
• Cholecystitis
• Malabsorption syndromes
• Other neuroendocrine tumors – VIPoma, carcinoid
• Gastroenteritis (chronic or relapsing)

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
• Age – median is 40s
• Sex – M<F, 1:2
• Occurrence – usually sporadic

Risk Factors

• Genetic
  • Small percentage associated with multiple endocrine neoplasias type 1 (MEN1)
  • 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
  • Diabetes mellitus – occurs in ~10% of intestinal and 75% of pancreatic tumors
  • Cholelithiasis – occurs in 60% of pancreatic and ~30% of intestinal tumors
  • Diarrhea/steatorrhea
• 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

Treatment

• Symptomatic relief
• Somatostatin analogues
• Resection is treatment of choice

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