Gastrointestinal neuroectodermal tumour: A case report of a rare Tumour/Tumeur neuroectodermique gastro-intestinale : etude de cas d'une tumeur rare

Gastrointestinal neuroectodermal tumours (GNET) are rare mesenchymal neoplasms, originally described under the name clear cell sarcoma-like tumour of the gastrointestinal tract (CCSLTGT). GNETs have a poor prognosis and often reoccur as metastatic disease after primary resection. The differential diagnosis of GNET includes gastrointestinal stromal tumour (GIST), clear cell sarcoma of the gastrointestinal tract (CCS-GI), and melanoma. GNET are characterized by a sheet-like or nested population of cells which can be epithelioid or spindled. Immunohistochemistry demonstrates a strong diffuse staining for S100. Melanocytic makers, markers for GIST, and epithelial markers are negative. The Ewing sarcoma breakpoint region 1 gene (EWSR1) is frequently rearranged in GNET cases although these rearrangements are neither diagnostic for, nor specific to, GNET. This report describes a case of GNET that presented as a small bowel obstruction in a 65-year-old man and, later, as metastatic disease in the liver. The tumours in this case comprised sheets of poorly differentiated spindle and epithelioid cells with an immunohistochemical profile consistent with GNET. The case did not, however, show EWSR1 gene rearrangement. GNET is a rare and aggressive tumour with a broad differential. It can be difficult to diagnose especially if the common features are not present. Keywords: Gastrointestinal, neuroectodermal, mesenchymal, tumour, EWSR1, clear cell, sarcoma-like. Les tumeurs neuroectodermiques gastro-intestinales (TNEGI) sont des neoplasmes mesenchymateux rares d'abord qualifies de pseudosarcomes a cellules claires du tube digestif. Les TNEGI, qui reapparaissent souvent sous forme de maladie metastatique apres une resection primaire, sont associees a un pronostic defavorable. Le diagnostic differentiel des TNEGI comprend la tumeur stromale gastro-intestinale (TSGI), le sarcome a cellules claires du tube digestif et le melanome. Les TNEGI se caracterisent par une population de cellules epithelioi'des ou fusiformes organisees en feuillets ou en nids. L'immunohistochimie revele une coloration intense et diffuse pour S100. Les marqueurs melanocytaires, les marqueurs associes a la TSGI et les marqueurs epitheliaux sont negatifs. Chez les patients atteints de TNEGI, il est frequent d'observer le rearrangement du gene EWSR1 (region 1 du point de rupture du sarcome d'Ewing), bien qu'il ne s'agisse pas d'une caracteristique diagnostique ou d'un trait propre a ce genre de tumeurs. Ce