BACKGROUND: This article presents the results of histological, immunohistochemical,and ultrastructural examinations of embryonal rhabdomyosarcoma. MATERIAL/METHODS: 20 tumors were testedhistologically, 13 immunohistochemically, and 5 under electron microscopy. RESULTS: We found that incases when the entire tumor or large specimens were obtained for estimation, it was possible by examiningmany areas of the neoplasm to establish a diagnosis on the basis of testing paraffined sections, routinelyHE stained. Our evaluation of the value of certain additional histological methods indicated only slightdiagnostic usefulness for tumors of this kind. Among the immunohistochemical methods we evaluated, thedesmin assay had the greatest practical applicability, due to the fact that this antigen is also expressedin highly immature cells; in second place was myoglobin. Differences are pointed out in the results obtainedby assaying myoglobin using DAB and the DAKO kit. Ultrastructural examinations revealed myofilamentsof myosin and actin in all types of cells, including immature cells. Particular attention is drawn tothe possibility of using material fixed in formalin for ultrastructural examination. The preservationof intact myofilaments in material prepared in this way constitutes an essential diagnostic aid. CONCLUSIONS:In diagnosing embryonal rhabdomyosarcoma the most useful examination, apart from histological examination,is electron microscopy, followed by immunomorphological examination.

Keywords: Adolescent, Child, Child, Preschool, Cytoplasm, Microscopy, Electron, Rhabdomyosarcoma, Embryonal, Sarcoma