Neuroendocrine Tumors

Definition

Neuroendocrine tumors (NETs) are a heterogeneous group of neoplasms arising from neuroendocrine cells, capable of producing peptides and hormones that can cause distinct clinical syndromes. They can occur in various organs including the gastrointestinal tract, pancreas, and lungs.

Epidemiology

• Incidence: ~5 per 100,000 per year, increasing due to improved detection
• Can occur at any age but more common in adults aged 50–60 years
• Slight male predominance
• Most common sites: small intestine, pancreas, lung, appendix, rectum
• Rare familial syndromes: MEN1, MEN2, Von Hippel-Lindau

Etiology

• Mostly sporadic; some hereditary syndromes (MEN1, MEN2, VHL)
• Genetic mutations: MEN1, RET, VHL, NF1, TSC1/2
• Environmental factors are not clearly defined
• Chronic atrophic gastritis or Zollinger-Ellison syndrome increases risk for gastric NETs
• Pancreatic NETs may be functional (hormone-secreting) or non-functional

Pathophysiology

• Originates from neuroendocrine cells capable of hormone secretion
• Tumors may secrete serotonin, gastrin, insulin, glucagon, VIP, or other peptides
• Local invasion and distant metastases via lymphatics and bloodstream
• Functional NETs produce hormone-related syndromes (e.g., carcinoid syndrome, hypoglycemia)
• Tumor grade (Ki-67 index, mitotic rate) determines aggressiveness