Carcinoid Syndrome
A set of symptoms (flushing, diarrhoea, wheezing) caused by hormones secreted by neuroendocrine tumours, particularly serotonin. Somatostatin analogues (octreotide, lanreotide) effectively control carcinoid syndrome symptoms by suppressing tumour hormone secretion.
Technical Context
Carcinoid syndrome occurs when functional midgut NETs (primarily ileal) metastasise to the liver — hepatic metastases release serotonin and other vasoactive substances directly into the systemic circulation (bypassing hepatic first-pass metabolism). Symptoms: flushing (85-90%, episodic facial/upper body redness), diarrhoea (80%, watery, non-bloody — serotonin stimulates intestinal secretion and motility), bronchospasm (15%), and carcinoid heart disease (20-50% — serotonin-mediated endocardial fibrosis causing right-sided valve disease, particularly tricuspid regurgitation and pulmonary stenosis). Diagnosis: elevated 24-hour urinary 5-HIAA (5-hydroxyindoleacetic acid, serotonin metabolite) and/or elevated chromogranin A. Treatment: octreotide LAR or lanreotide autogel suppress serotonin secretion and control symptoms in approximately 70-80% of patients. Telotristat ethyl (tryptophan hydroxylase inhibitor) is added for breakthrough diarrhoea. SSA therapy also slows tumour progression (antiproliferative effect demonstrated in PROMID trial for octreotide LAR and CLARINET trial for lanreotide).