[Ultrastructural and immunohistochemical observations on alveolar rhabdomyosarcoma].

One case of alveolar rhabdomyosarcoma appearing like an undifferentiated tumor by light microscopy is reported. Specific ultramicroscopic features of sarcomere containing Z line structures, thick and thin myofilaments with hexagonal arrangements in the cross section were noted in the cytoplasm of some individual malignant cells, thus establishing the diagnosis of rhabdomyosarcoma. Some of the tumor cells were positive to peroxidase-anti-peroxidase (PAP) immunohistochemical stain of anti-serum by anti-myosin. In the present paper, the ultrastructural features and differential diagnosis of poorly differentiated rhabdomyosarcoma are also discussed.