The epidermal growth factor receptor HER2 is not a major therapeutic target in Ewing sarcoma

Background: Although chimeric EWS gene and Ets gene fusions are pathognomonic of Ewing sarcoma (ES) and primitive neuroectodermal tumors (PNET), the molecular pathogenesis of these pediatric malignancies is poorly understood. Recently, the human epidermal growth factor (HER)-2 receptor, which plays an important role in the biology of certain epithelial cancers, has been implicated in ES tumor cell line growth and chemosensitivity. Materials: To investigate whether HER2 might be a rational target for ES/PNET therapy, five ES cell lines and 13 archival primary ES/PNET samples were examined by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) for evidence of HER2 overexpression. Results: Although several ES cell lines demonstrated modest constitutive HER2 expression by immunoblot, none of the ES cell lines or primary tumor samples showed evidence of HER2 overexpression by IHC or HER2 gene amplification by FISH. Moreover, treatment of human ES cell lines with the HER2-targeted agent trastuzumab (Herceptin) had little effect on cell survival, proliferation, or growth in semi-solid medium. Conclusions: These results suggest that HER2 is not a biologically or therapeutically important pathway in ES/PNET.