Myogenin

Immunohistochemistry was performed on all cases, either at the time of original diagnosis or for the purposes this study. Whole-slide sections of formalin-fixed, paraffin embedded tumor tissue were cut at five-micron thickness, deparaffinized, and subjected to antigen retrieval using 10 mM citrate buffer at 92°C for 30 minutes. Immunohistochemistry was performed on all cases using antibodies for S100 (Ventana Medical Systems, Tucson, AZ), either Smooth Muscle Actin (Ventana) or Calponin (Dako, Carpinteria, CA), SOX10 (BioCare Medical, Concord, CA), Desmin (Dako), and β-catenin (BD Biosciences, San Jose, CA). In addition, for a subset of cases (n=6), PAX3 (Bioss Inc., Wolburn, MA) immunohistochemistry was also performed. Depending on tissue availability, immunohistochemistry was also performed in most cases using antibodies for myogenin (Ventana) and Factor XIIIa (Cell Marque, Rocklin, CA). All immunohistochemical signals were visualized using the Ultra view polymer detection kit (Ventana Medical Systems, Inc. Tucson, AZ) on a Ventana BenchmarkXT autostainer (Ventana). Staining was performed according to manufacturer's instructions in the presence of appropriate controls. “Focal” immunoreactivity was regarded as immunostaining in <10% of tumor cells.