Granin-derived peptides as diagnostic and prognostic markers for endocrine tumors.

Chromogranin A-like immunoreactivity (CgA-LI) has been, and remains, the most widely used diagnostic and prognostic marker for endocrine tumors. The availability of assay kits combined with moderately high sensitivity and specificity has meant that there has been no great incentive to develop alternative markers. However, circulating concentrations of CgA-LI are elevated in several non-neoplastic diseases and in patients receiving acid-suppression therapy which may lead to false positive diagnosis. Additionally, certain endocrine tumors, such as rectal carcinoids, do not express the CgA gene so that there is a need for additional markers to complement CgA measurements. Plasma concentrations of the CgA-derived peptide, pancreastatin, measured with antisera of defined regional specificity, have a prognostic value in patients with metastatic midgut carcinoid tumors receiving somatostatin analog therapy or hepatic artery chemoembolization. Other CgA-derived peptides with potential as tumor markers are vasostatin-1, WE-14, catestatin, GE-25, and EL-35 but their value has yet to be fully assessed. Circulating concentrations of chromogranin B-like immunoreactivity (CgB-LI) are not elevated in non-neoplastic diseases and measurements of CCB, the COOH-terminal fragment of CgB, may be useful as a biochemical marker for neuroendocrine differentiation in lung tumors. Antisera to the secretogranin II-derived peptide, secretoneurin detects carcinoid tumors of the appendix with greater frequency than antisera to CgA and are of value in identifying therapy-resistant carcinoma of the prostate (clinical stage D3). Measurement of concentrations of a second secretogranin II-derived peptide, EM-66 in tumor tissue has been used to differentiate between benign and malignant pheochromocytoma. These examples point to a limited although potentially valuable role for granin-derived peptides as tumor markers.