Immunophenotypic profile of anti-apoptotic and neuroectodermal differentiation pathways in the Ewing’s Family of tumors (EFT)

Running title: anti-apoptotic and neuroectodermal pathways in Ewing family of tumors Supported by grant 01/0673 fom FIS (Madrid) and PROTHETS (EC Contract number 503036). ABSTRACT Aims An important criteria for EFT is that it originates from a primitive committed cell with neuroectodermal capacity. The degree of neural differentiation within EFT, as measured with morphological features and expression of neural markers, delimits two groups of EFT: Ewing´s sarcoma (ES) and peripheral primitive neuroectodermal tumor (pPNET). Molecules such as c-kit and its ligand (Stem cell factor SCF), CD95 (FAS), CD95L (FASL), IGF-IR, protect EFT cells from 2 apoptosis whereas erb-B2 results essentially in the maturation of primitive committed neuroectodermal cells. The aim of the present study was to analyse the expression in vivo of such molecules in EFT. Methods and results 45 cases of EFT (23 ES and 22 pPNET) were analysed following the immunohistochemical LSAB method, with antigen retrieval heating with autoclave and cytrate buffer pH 6.0 and the following primary antibodies: FAS (APO-CD 95), FAS-L, c-kit, SCF, IGF-IR (Santacruz Biotech), and c-erbB2 (DAKO). The expression was evaluated independently by the three authors, and the final score (0 to 3+) was based on the intensity and percentage of positive cells. High expression of c-kit/SCF (2+,3+) was detected in 28/45 cases of EFT (62.2%) ,whereas FAS-FAS-L and IGF-IR was observed in 16/45 (37.7%) and 9/45 (20%) respectively. Regarding the neuroectodermal pathway, membranous and cytoplasmic expression of c-erbB2 was observed in 9/45 (20%) ES and pret cases, regardless of the morphological and immunohistochemical expression of conventional neural markers. Conclusions C-kit/SCF could be an essential pathway of anti-apoptotic and proliferative advantage, while c-erbB2 does not seem to play an important role in the neuroectodermal differentiation pathway in EFT cells.