Most of the neuroendocrine tumours produce and secrete a large number of
peptide hormones and
amines. Each of these substances cause a specific clinical syndrome:
carcinoid, Zollinger-Ellison, hyperglycaemic,
glucagonoma and
WDHA syndrome. Specific markers for these syndromes are basal and/or stimulated levels of: urinary-5-HIAA, serum or plasma
gastrin,
insulin,
glucagon, and VIP, respectively. About 1/3 of neuroendocrine tumours belong to the so-called "non-functioning" tumours. Therefore, general markers such as
chromogranin A,
pancreatic polypeptide, serum neuronspecific
enolase and subunit of
glycoprotein hormones have been used for screening purposes in patients without distinct clinical
hormone related syndromes. Among these general tumour markers
chromogranin A, although its precise function is not yet established, has been shown to be a very sensitive and specific
serum marker for various types of neuroendocrine tumours. This is because it may also be increased in many cases of less well differentiated tumours of neuroendocrine origin that do not secrete known
hormones. Then
chromogranin A is considered the best general neuroendocrine serum or plasma marker available at the moment and is increased in 50-100% of patients with various neuroendocrine tumours.
Chromogranin A serum or plasma levels reflect tumour load and may be an independent marker of prognosis in patients with midgut
carcinoids.