Immunocytochemistry of rhabdomyosarcoma. The use of four different markers.

Fast myosin and slow myosin are specific markers of skeletal muscle, in addition to myoglobin. This study of 15 specimens of rhabdomyosarcomas from 13 patients using specific antisera for the three markers as well as for desmin led to positive findings in all cases with at least one antiserum. Desmin was present in all cases; fast myosin and myoglobin were present in 10 cases each. Slow myosin was present in six cases. It appears that the combination of several markers is helpful in differentiating rhabdomyosarcomas from other tumors. The markers considered were generally more abundant in neoplastic elements with large amounts of cytoplasm. This finding suggests that the larger cells of rhabdomyosarcomas are more differentiated than smaller rhabdomyoblasts, which were often negative with some of the antisera used.