Neuroendocrine Tumors and Associated Symptoms

Chronic and Nocturnal Diarrhea

Carcinoid syndrome causes diarrhea in approximately 50-70% of patients at diagnosis, typically occurring with hepatic metastases that allow bioactive products to bypass hepatic metabolism and enter systemic circulation, as recommended by the National Comprehensive Cancer Network 1, 2
VIPomas produce profuse secretory diarrhea (>1 liter/day) in 100% of cases, often accompanied by dehydration and hypokalemia, with serum VIP levels ranging from 675-965 pg/mL compared to normal values <170 pg/mL, according to the British Society of Gastroenterology 3
Gastrinomas cause diarrhea in approximately 50-65% of patients through gastric acid hypersecretion (Zollinger-Ellison syndrome), with one-half of patients presenting with chronic diarrhea as the chief complaint rather than peptic ulcer symptoms, as stated by the European Neuroendocrine Tumor Society 4

The National Comprehensive Cancer Network recommends measuring 24-hour urinary 5-HIAA (sensitivity and specificity 88% for carcinoid syndrome), ensuring adherence to dietary restrictions 3
The European Neuroendocrine Tumor Society suggests checking fasting serum gastrin if acid reflux and diarrhea coexist; levels >1000 pg/mL suggest gastrinoma, though comparable elevations occur with pernicious anemia, atrophic gastritis, or potent acid suppression 3
The British Society of Gastroenterology recommends measuring serum VIP during a diarrheal episode if secretory diarrhea exceeds 1 liter/day 3
The American Gastroenterological Association suggests measuring chromogranin A as a general NET marker, particularly useful in gastric carcinoids with metastases 7

The National Comprehensive Cancer Network and the British Society of Gastroenterology guidelines make no mention of elevated ferritin or B12 as features of NETs, and elevated ferritin suggests inflammatory processes, iron overload, or hepatic dysfunction from metastatic disease rather than direct NET effects 1, 5, 6, 4, 3, 7
Elevated B12 is not a documented consequence of NET hormone secretion and warrants investigation for alternative causes (myeloproliferative disorders, liver disease, renal failure), as stated by the European Neuroendocrine Tumor Society 6