Somatostatinoma

Henry William Taylor, MD
The Operative Review of Surgery. 2023; 1:175-181.

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Table of Contents

Pathophysiology
Presentation
Diagnosis
Treatment

References

Pathophysiology

Also Known as “Somatostatin-Secreting Tumors”, “Somatostatin-Secreting Pancreatic Neoplasm”, or “SS-omas”

Definition 1

Location 2-6

  • Pancreas (40-55%) – Most Common
  • Duodenum (45-50%)
  • Other Rare Locations:
    • Jejunum
    • Stomach
    • Colon
    • Rectum
    • Lung
    • Kidney
    • Liver

Pancreatic Distribution and Size

  • Most Common in the Head (56%) 3
  • Most Often Solitary Masses 3,7
  • Usualluy Large at Time of Diagnosis
  • Average Diameter: 3
    • 5-6 cm in Pancreas
    • 2-5 cm in Duodenum

Malignancy

  • Most are Malignant (75-78%) 7-9
  • Majority Have Metastases at Diagnosis (70-92%) 7-9
  • Associated Syndromes:
    • 35-45% of Pancreatic Somatostatinomas are Associated with Multiple Endocrine Neoplasia Type 1 (MEN-1) 10
      • Overall One of the Least Common PNETS in MEN-1 (< 1%) 7,10,11
    • 50% of Duodenal Somatostatinomas are Associated with Neurofibromatosis Type 1 (NF-1/von Recklinghausen Disease) 7,9,12
      • Less Likely to Metastasize than Spontaneous Duodenal Somatostatinomas 7
    • Has Also Been Associated with von-Hippel Lindau Syndrome 13,14

Epidemiology

  • Median Age: 54 Years 3
  • Equal Gender Distribution 7

Duodenal Somatostatinoma on Endoscopy (Arrow Point to Ampulla of Vater) 15

Presentation

Somatostatinoma Syndrome

  • Syndrome of Symptoms Associated with the Overproduction of Somatostatin
  • Triad: 16
    • Diabetes/Glucose Intolerance
    • Cholelithiasis
    • Diarrhea/Steatorrhea
  • Less Commonly Seen (19% if in Pancreas or 2% if in Duodenum) 2,17

Additional Symptoms 10,16,18,19

  • Abdominal Pain (50%) – Most Common Symptom
  • Weight Loss (20-30%)
  • Hypochlorhydria
  • Local Complications:
    • Abdominal Pain
    • Obstructive Jaundice
    • GI Bleeding/Anemia

Diagnosis

Diagnosis

  • If Somatostatinoma Syndrome Present:
    • High Fasting Plasma Somatostatin (At Least Thee Times the Upper Limit of Normal) 18
    • Biopsy Not Required but Can Be Used for Grading 20
  • If Somatostatinoma Syndrome is Not Present (Most Common):
    • Most Commonly Detected in the Workup of a Pancreatic or Duodenal Mass
    • Biopsy Histopathology Demonstrates Well-Differentiated Islet Cells that Stain Positive for Somatostatin 21

TNM Staging

Localization

  • Initial Imaging: Noninvasive (CT or MRI) 23,24
  • Somatostatin Receptor Imaging 23-26
    • Consider if Initial Imaging Fails to Localize
    • Options:
      • Somatostatin (Octreotide) Receptor Scintigraphy (SRS) – Classic Test Used
      • Functional PET Scan (Ga-68 DOTATATE) – Becoming More Prevalent with Higher Sensitivity
  • If Noninvasive Imaging Fails: Invasive Imaging
    • Endoscopic Ultrasound (EUS) – Generally Preferred Next Step 27
    • Selective Visceral Angiography 28,29

PNET on Imaging: (A) CT, (B) EUS, (C) SRS, (D) Functional PET 30

Treatment

Surgical Resection (Treatment of Choice)

  • Definitive Treatment: Surgical Resection 31,32
    • Head/Neck: Pancreaticoduodenectomy
    • Body/Tail: Distal Pancreatectomy (Concurrent Splenectomy if Malignancy is Suspected)
    • Entire Pancreas: Total Pancreatectomy
  • May Consider Enucleation for Small Tumors (< 2-3 cm) – Controversial Due to High Malignancy Rates
    • Additional Requirements: Single Lesion, ≥ 2-3 mm From the Main Pancreatic Duct, Well-Encapsulated, and No Local Invasion
  • Due to High Rates of Metastases, Surgical Resection is Most Often Not Feasible 7-9

Liver-Directed Therapy

  • Resection of Metastases if Able 33,34
  • Radiofrequency Ablation (RFA) or Cryoablation 33-35
  • Hepatic Artery Embolization 36,37

Additional Options in Surgically Unresectable Disease

  • Somatostatin Analogs (Octreotide/Lanreotide) 38,39
    • Can Also Be Use Preoperatively to Control Symptoms
  • Other Molecular-Targeted Agents:
    • Everolimus 40
    • Sunitinib 41
  • Peptide Receptor Radionuclide Therapy (PRRT) 42
  • Chemotherapy 24,43-45
  • Radiation Therapy 46,47
    • Pancreatic Neuroendocrine Carcinomas Were Previously Considered to be Resistant to Radiation

References

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