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

Abstract

Background: Most neuroendocrine tumors express chromogranin A (CgA). The posttranslational processing 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 treatment 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 sequencespecific assays for CgA were evaluated on plasma samples from patients with neuroendocrine tumors and small-cell lung carcinomas. Furthermore, we investigated whether the CgA plasma concentrations correlated with the tumor burden. Results: Size-exclusion chromatography of plasma showed that CgA immunoreactivity mainly consisted of high-molecular-weight forms, indicating that neuroendocrine tumors may secrete large amounts of poorly processed CgA. Accordingly, trypsination of plasma from 54 patients with neuroendocrine tumors or smallcell lung carcinomas increased the CgA(3403) immunoreactivity up to 500-fold. Both the CgA(3403) assay and the PIA measured significantly higher plasma concentrations in patients with very extensive disease than in patients with less widespread disease. The diagnostic

Somatostatin-Immunoreactive Pancreaticoduodenal Neuroendocrine Neoplasms: Twenty-Three Cases Evaluated according to the WHO 2010 Classification

“…The upper CgA reference level was 130 pmol/l. Both methods are described elsewhere [20,21,22]. Gastrin concentrations in plasma were measured using antibody 2604, which binds the bioactive sequence of all amidated gastrins.…”

Peptide Receptor Radionuclide Therapy with ⁹⁰Y-DOTATOC and ¹⁷⁷Lu-DOTATOC in Advanced Neuroendocrine Tumors: Results from a Danish Cohort Treated in Switzerland

“…Progressive disease was assumed by the referring physicians if at least one of the following imaging modalities and blood tests gave rise to suspicion of increasing tumor load: growing or new lesions on computed tomography (CT), new lesions on SRS, or increasing tumor marker levels of plasma chromogranin A (CgA) [23,24]. The assessment was typically based on a combination of all three.…”

Cell-Specific Precursor Processing

“…In contrast, PIA did not improve the diagnostic sensitivity significantly for gastrinoma patients with consistently enhanced concentrations of carboxyamidated gastrin in plasma (Jørgensen et al 1998). For both proCCK progastrin and chromogranin A we could, however, show that PIA provides a significantly more accurate measure of the tumor burden for each individual patient than conventional RIA measurements (Bardram 1990;Børglum et al 2007;Reubi et al 2004). …”

“…In accordance with the general design, we have developed specific radioimmunoassays for fragments of human progastrin, chromogranin A, proCCK, proBNP, and proCNP (Bardram and Rehfeld 1988;Paloheimo and Rehfeld 1994;Goetze et al 2002;Nielsen et al 2005;Børglum et al 2007). These sequences follow trypsinsensitive arginyl or lysyl residues and contain a tyrosyl residue at the C-terminus.…”