Although
chromogranin A (CgA) is widely distributed in
neuroendocrine tumors, the distribution of
chromogranin B (CgB) has not been elucidated.
Hormones produced by
tumors are sometimes prohormones and not necessarily bioactive
hormones. Prohormones have to be processed into bioactive
peptides by
prohormone convertases (PCs), and some of them have to be amidated by peptidylglycine a-amidating
monooxygenase (PGM). Whether PCs and PGM are present or not in
tumors may explain why some
tumors are functioning and some are nonfunctioning. We investigated 45
carcinoids and 16 pancreatic endocrine
tumors. Of the
carcinoids, CgA was expressed in most of the
tumors, except for the rectal and ovarian
carcinoids, which expressed CgB strongly. The expressions of PC2, PC3, and PGM were 31%, 100%, and 87%, respectively. In the pancreatic
tumors, CgA was expressed in all
tumors, whereas CgB was not expressed in any
tumor. The expressions of PC2, PC3, and PGM were 63%, 88%, and 63%, respectively. PC3 was expressed in all of the functioning
tumors but not in two of the four nonfunctioning
tumors. PC2 and PGM were not expressed in three of the four nonfunctioning
tumors. In conclusion, expression of CgA and CgB was different depending on the
tumor location. High frequency of PCs and PGM may explain why even nonfunctioning
tumors produce some inconspicuous
peptides.