Islet Cell Tumors

Snapshot

A 50-year-old woman presents to her primary care physician complaining of prolonged episodes of watery diarrhea, fatigue, and muscle weakness. Laboratory results demonstrate that she is hypokalemic with a normal anion gap metabolic acidosis. Fasting VIP plasma levels confirmed the diagnosis of a VIPoma (islet cell tumor) and octreotide was started for treatment.

Introduction

Glucagonoma

Insulinoma

Neoplasm of β-islet cells
- most common islet cell tumor
Association with MEN I
Presentation
- symptoms
  - mental status alterations
- physical exam
  - hypoglycemia
Evaluation
- serology
  - ↑ insulin
  - ↑ C-peptide
    - important to distinguish patients who are injecting themselves with insulin (would be low)
Treatment
surgery

Somatostatinoma

Neoplasm of δ-islet cells
- somatostatin is normally an inhibitor of most GI hormones
Presentation
- symptoms
  - achlorhydria
    - blockage of gastin release
  - cholelithiasis
    - blockage of CCK release
  - steatorrhea
    - blockage of secretin release
  - diabetes mellitus
    - blockage of GIP release
Treatment
- surgery
- medical
  - combination chemotherapy
    - 5-fluorouracil
    - streptozotocin
alkylating agent that targets cells arising from Islets of Langerhans

VIPoma

Neoplasm that produces ectopic vasoactive intestinal peptide (VIP)
- normal functions of VIP
  - activates cAMP intestinal epithelial cells results in secretory diarrhea
  - vasodilation
  - inhbition of gastric acid secretion
  - stimulation of intestinal secretion
  - smooth muscle cell relaxation (lower esophageal sphincter)
Presentation
- symptoms
  - facial flushing
  - secretory diarrhea (also called pancreatic cholera)
  - achlorhydria
Evaluation
- serology
  - hypokalemia
  - normal anion gap metabolic acidosis
  - resembles labs of other secretory diarrheas
  - hypercalcemia
Treatment
- surgery
- medical
octreotide

Nonfunctioning tumors