Processing-Independent Quantitation of Chromogranin A in Plasma from Patients with Neuroendocrine Tumors and Small-Cell

ing of neuroendocrine proteins such as CgA is often specific for the individual tumor. To cope with this variability and improve tumor diagnosis, we developed a processing-independent analysis (PIA) method to measure the total CgA product. Methods: For PIA, samples underwent trypsin treat-ment followed by measurement of CgA by the “CgA(3403) ” assay, in which the antiserum binds an epitope starting at amino acid 340 of CgA and including amino acid residues located in the C-terminal direction. The diagnostic accuracy of the CgA PIA and 3 sequence-specific assays for CgA were evaluated on plasma sam-ples from patients with neuroendocrine tumors and small-cell lung carcinomas. Furthermore, we investi-gated whether the CgA plasma concentrations corre