Abstract

Small round cell tumors such as neuroblastoma, rhabdomyosarcoma, Ewing's tumor, malignant lymphoma and small cell carcinoma are often confused clinically and histologically. To clarify the similarites and differences and to get more information on the histogenesis among the small round cell tumors, we examined histological, immunohistochemical and ultrastructural features of ten cases of neuroblastomas, twenty Ewing's tumors, ten embryonal rhabdomyosarcomas and twelve small cell carcinomas in children and young adults. Antibodies against desmin, vimentin, cytokeratin, neuron-specific enolase, synaptophysin, neurofilament, S-100 protein, chromogranin and HBA 71 were used in biotin streptavidin procedures. The results of the immunohistochemical and electron microscopical examinations yielded virtually identical findings in each group as followings. 1) Among the twenty cases of Ewing's tumors, eighteen cases were positive in staining for HBA-71. The staining for HBA-71 was negative in neuroblastoma, embryonal rhabdomyosarcoma and small cell carcinoma. 2) Neuroblastomas had marked interdigitating cytoplasmic processes containing many microtubules and dense-core secretory granules, however, they were sparse and rare in Ewing's tumor. 3) Embryonal rhabdomyosarcoma showed actin-myosin bundles. According to differentiation, well differentiated rhabdomyosarcoma exhibited Z-band materials and external lamina. 4) Neuroblastoma showed ultrastructural evidence of a neuronal differentiation, but neuronal differentration is a sparse and rare in Ewing's tumor. This ultrastructural feature strengthens the hypothesis that Ewing's tumor is derived not only from an undifferentiated neuroectodermal stem cell but from primitive cell of neuroectodermal origin.

• Keywords: Small round cell tumor;Immunohistochemistry;Ultrastructure