Neuroendocrine Tumors

NETs Overview - Tumor Genesis Gems

• Definition: Neoplasms from neuroendocrine (APUD) cells.
• Origin: Enterochromaffin (Kulchitsky) cells.
• Common Sites: GIT (commonest), pancreas, lung.
• Classification:
  • Functional (hormone+) / Non-functional.
  • WHO Grade (Ki-67/mitoses):
    • G1: Ki-67 <3%, Mitoses <2/10HPF
    • G2: Ki-67 3-20%, Mitoses 2-20/10HPF
    • G3: Ki-67 >20%, Mitoses >20/10HPF

⭐ Midgut NETs with liver mets most often cause carcinoid syndrome (flushing, diarrhea, bronchospasm).

Carcinoid Syndrome - Crimson Tide Tales

• Pathophysiology: From vasoactive substances (serotonin, kallikrein, prostaglandins, histamine) from NETs, bypassing liver metabolism.
• Classic Triad: Episodic cutaneous flushing (crimson), secretory diarrhea, and bronchospasm.
  • 📌 Mnemonic FDR: Flushing, Diarrhea, Right-sided heart lesions.
• Carcinoid Heart Disease: Right-sided valvular fibrosis causing Tricuspid Regurgitation (TR) and Pulmonary Stenosis (PS).
• Diagnosis: Elevated 24-hour urinary 5-hydroxyindoleacetic acid (5-HIAA), >25 mg/24h.
• Triggers: Alcohol, stress, anesthesia, certain foods (aged cheese, red wine).

⭐ Octreotide (somatostatin analog) is used for symptomatic treatment and can also help localize tumors via OctreoScan.

Pancreatic NETs - Pancreas's Peculiar Posse

⭐ Octreotide scan (Somatostatin Receptor Scintigraphy, SRS) aids localization for most pNETs (gastrinoma, glucagonoma, VIPoma, somatostatinoma); insulinomas often require other localization studies due to variable receptor expression. Insulinomas are the most common pNET overall, but gastrinomas are most common in MEN1.

NET Diagnosis & Staging - Clue Cracking & Counts

• Biochemical Markers:
  • Chromogranin A (CgA): General NET marker.
  • Specific hormones (e.g., insulin, gastrin) if tumor is functional.
• Imaging Pathway:
  • CT/MRI: Initial localization.
  • Somatostatin Receptor Scintigraphy (SRS): Octreoscan.
  • ⁶⁸Ga-DOTATATE PET/CT: Gold standard for SSTR imaging.
  • Endoscopic Ultrasound (EUS): For pancreatic/GI NETs.
• Biopsy & Grading:
  • Histology confirms diagnosis.
  • Grading (Ki-67 index, mitotic rate): G1 (Ki-67 $\le$2%), G2 (Ki-67 3-20%), G3 (Ki-67 $>$20%).

⭐ ⁶⁸Ga-DOTATATE PET/CT offers superior sensitivity over Octreoscan for detecting SSTR-positive NETs and is crucial for staging and PRRT planning.

NET Management - Taming the Tiny Terrors

• Surgery: Primary curative option for localized disease. Resection of primary and, if feasible, metastases.
• Somatostatin Analogs (SSAs): Octreotide, Lanreotide.
  • Control hormonal syndromes (e.g., carcinoid).
  • Anti-proliferative in well-differentiated NETs.
• Peptide Receptor Radionuclide Therapy (PRRT):
  • $^{177}$Lu-DOTATATE targets SSTR-positive tumors with radiation.
• Targeted Molecular Therapies:
  • Everolimus (mTOR inhibitor) for advanced pNET, GI, lung NETs.
  • Sunitinib (tyrosine kinase inhibitor) for advanced pNETs.
• Chemotherapy: Streptozocin, Temozolomide.
  • Reserved for high-grade, aggressive, or rapidly progressive NETs, especially poorly differentiated neuroendocrine carcinomas (NECs) and some pNETs.

⭐ Peptide Receptor Radionuclide Therapy (PRRT) with $^{177}$Lu-DOTATATE has shown significant improvement in progression-free survival for patients with advanced, progressive, SSTR-positive midgut NETs.

High‑Yield Points - ⚡ Biggest Takeaways

• Carcinoid syndrome presents with flushing, diarrhea, bronchospasm, and right-sided cardiac lesions.
• Diagnose carcinoid syndrome via elevated urinary 5-HIAA levels.
• Chromogranin A (CgA) is a sensitive tumor marker for most NETs.
• Somatostatin analogues (e.g., Octreotide) are key for managing symptomatic NETs.
• Pancreatic NETs (e.g., gastrinoma, insulinoma) are strongly associated with MEN 1 syndrome.
• Gastrinomas (ZES) cause refractory peptic ulcers and markedly high gastrin levels.
• Insulinomas characteristically manifest with fasting hypoglycemia and Whipple's triad.