Investigations

General markers of neuroendocrine tumours

• chromogranin A (CgA)
  • a secretory granule, is located alongside specific hormones in large dense-core vesicles of neuronal and neuroendocrine cells
  • CgA is raised in 99% of metastatic carcinoid tumours
• other general staining markers include pancreatic polypeptide, neuron-specific enolase, peptide histidine-methionine and human chorionic gonadotrophin subunits

Specific markers of carcinoid tumours

• carcinoid tumours secrete a variety of catecholamines, including serotonin. Diagnosis can be made on the basis of a raised 24 hour urinary level of 5-HIAA - a breakdown product of serotonin; or by whole blood serotonin
  • other urinary markers include neuropeptide K, substance P and other tachykinins
  • urinary hydroxyindole acetic acid (5HIAA) and neuropeptide K show high sensitivity in midgut carcinoid - these markers have less diagnostic usefulness in foregut and hindgut carcinoid
• if a diagnosis of carcinoid is suspected with normal baseline urinary testing, the pentagastrin test with measurements of plasma tachykinins is a useful diagnostic measure

Other investigations:

• radiological localisation of carcinoid tumour
  • somatostatin-receptor-scintigraphy
    • sensitivity 90% and specificity 80%
  • CT
    • may be used preoperatively for localizing tumours- however difficulty detecting tumours <1cm
• a liver ultrasound scan or CT scan may show evidence of secondaries in the liver.

Reference:

1. Endocr Relat Cancer. 2004 Mar;11(1):1-18.