|
|
Amin Sabet, M.D.
04-07-2010
- Rare somatostatin-producing neuroendocrine tumors (NETs) which arise primarily in the pancreas and duodenum
- Associated with diabetes since high somatostatin levels suppress insulin secretion (Gerich)
- Represent 1-2% of pancreatic islet cell tumors (He)
- Median age at diagnosis is 50 years (range 26-84 years) with equal sex distribution
- Greater than 50% arise in pancreas, two thirds of which are in head of pancreas
- Most extrapancreatic somatostatinomas arise in duodenum; rarely found as primary tumors of liver, colon, or rectum
- Most sporadic but minority can also be associated with MEN 1 syndrome.
- Duodenal somatostatinomas are associated with von Recklinghausen's disease (Neurofibromatosis type 1)
- Majority of somatostatinoma cases are malignant with metastases present at the time of diagnosis
- Leads to diabetes in majority of patients with pancreatic tumors; ~10% in intestinal tumors.
- In one case series, diabetes occurred in 36% of patients with somatostatinoma (6 pancreatic, 5 duodenal) (Moayedoddin).
- Often discovered during evaluation of patients with abdominal pain, weight loss, or jaundice. May be discovered as an incidental finding during imaging (86% pancreatic versus 41% of extrapancreatic somatostatinomas are >2cm) or during operation for an unrelated problem
- If the diagnosis is suspected based on symptoms, a preoperative fasting somatostatin level > 160 pg/mL (normal range 10-22 pg/mL) is suggestive of somatostatinoma
- Imaging studies may be structural (endoscopic ultrasound, CT, MRI) or functional (octreotide scan)
- Most common symptoms are non-specific: weight loss and abdominal pain
- May present with classic triad ("somatostatinoma syndrome"): diabetes mellitus (decreased insulin release), cholelithiasis (decreased cholecystokinin release with decreased gallbladder contractility), and diarrhea with steatorrhea (inhibition of pancreatic enzyme and bicarbonate secretion causing decreased intestinal absorption of lipids)
- Classic triad likely occurs only in about 10% of patients, more common in pancreatic tumors
- Duodenal somatostatinomas rarely cause this triad and may present with obstructive symptoms including pain and jaundice
- Diabetes can range from mild glucose intolerance (more common) to ketoacidosis (Jackson).
- Rare cases of somatostatinoma presenting with hypoglycemia attributed to inhibition of glucagon and growth hormone have been reported (He)
- Treatment of choice is surgical resection, which is the only potentially curative therapy
- Surgical debulking may improve symptoms in patients with metastatic disease
- For unresectable disease, the somatostatin analog octreotide may reduce plasma somatostatin levels and improve diarrhea, hyperglycemia, and weight loss
- Treatment with interferon alpha may alleviate symptoms in greater than 50% of patients with pancreatic NETs although tumor response rates are low (Schöber, Bajetta)
- Palliative chemoembolization of liver metastases may provide symptomatic improvement in selected patients with metastatic pancreatic NETs
- Results of systemic cytotoxic chemotherapy for metastatic pancreatic NETs have been disappointing, although some activity has been reported for combination streptozocin- and temozolomide-based regimens (Kouvaraki, Kulke)
- Hyperglycemia treated similar to other forms of diabetes; in addition, octreotide treatment will improve hyperglycemia.
- History and physical, imaging studies (CT/MRI), and fasting somatostatin level are recommended three and six months after surgical resection.
- Thereafter, clinical and biochemical surveillance are recommended every 6-12 months with imaging as clinically indicated.
- In one series of 44 patients with metastatic somatostatinoma, 5-year survival rate was 60% (Soga)
- Surgical management for pancreatic somatostatinomas (i.e. pancreatectomy) may lead to development of diabetes; glucose levels should be monitored regularly
- Diabetes is usually mild and more common in pancreatic somatostatinomas.
- Pancreatectomy for pancreatic somatostatinoma may also lead to development of diabetes.
|
|
