Specificity of Elevated Plasma EM66 Levels in Pheochromocytoma

Neuroendocrine tumors (NT) correspond to neoplasms that develop from endocrine and neuroendocrine cells scattered throughout the body. They are characterized by the occurrence, in their cytoplasm, of dense-core secretory vesicles containing hormones, neuropeptides and acidic proteins such as granins. The diversity of NT (from hypophysis, pancreas, adrenal, gastrointestinal tract) makes very difficult the identification and evaluation of the different types of tumors by the diagnostic and prognostic tools currently available. We have thus established a research program aimed at identifying new biological markers for the detection, the prognosis and the follow-up of NT by seeking in tumor and plasma samples of patients, granin-derived peptides. Our program was initiated on one type of NT : pheochromocytoma. These neoplasms correspond to tumoral chromaffin cells mainly originating from the adrenal medulla. It is considered that 10 % of pheochromocytoma patients will develop metastases and, currently, except in the presence of metastases, there are no means to predict malignancy of the tumor. We setup a radioimmunoassay of EM66 (a secretogranin II-derived peptide) that allowed us to demonstrate that (i) plasma concentrations of the peptide are significantly elevated in pheochromocytoma patients, (ii) combined with other biological tests EM66 measurement increase the diagnostic sensitivity for these neoplasms, (iii) after surgical removal of the tumor, plasma EM66 concentrations rapidly return to basal level and, (iv) intra-tumoral EM66 concentrations are higher in benign than in malignant pheochromocytomas (Yon et al., 2003, Guillemot et al., 2006). These results reveal that EM66 constitutes a novel tool for the diagnosis, prognosis and follow-up of pheochromocytoma. In the frame of a clinical use of an EM66 measurement test, it is necessary to evaluate the specificity of this marker. For instance, renal deficiency, hypergastrinemia, reduction of renal clearance, type A gastritis, Crohns disease, or proton-pump inhibitory treatment, lead to increase plasma chromogranin A (CgA) concentrations (false-positive cases). In addition, while hypertension account for one of the symptoms of pheochromocytoma patients, in essential hypertensive patients, CgA levels are higher than in normotensive individuals. The main objective of our clinical transfer research project consists to study the specificity of the measurement of EM66 as a diagnostic and prognostic marker of pheochromocytoma. This multicentric study will allow us to compare plasma EM66 levels in pheochromocytoma patients with a cohort of essential hypertensive patients. At the same time, in a long-range prospect, due to the lack of malignancy markers for these tumors, we will investigate if plasma or tumor EM66 levels are correlated to the differentiation status of pheochromocytomas, and if the expression level of a set of genes that we identified by a transcriptomic approach developed in the laboratory, is associated with the malignant status of the tumors. The stakes of this transfer research, involving our laboratory and the Center for Clinical Investigations (CIC) of Rouen and Lille, are to provide an easy and simple novel tool to practitioners and anatomo-pathologists for the screening, the evaluation and the follow-up of patients with neuroendocrine tumors.