Comparative phenotypes in rhabdomyosarcomas and developing skeletal muscle.

The morphological and immunohistochemical phenotypes of 51 rhabdomyosarcomas from young people have been described and contrasted with phenotypes in developing skeletal muscle from 20 fetuses and neonates. The tumours express markers in a cumulative and consistent sequence--vimentin, desmin, fast myosin, myoglobin--which evolves pari passu with morphological differentiation and follows the same pattern found in normal myogenesis. Changes in immunohistochemical phenotype are documented in residual and recurrent tumours excised after chemotherapy. The presumptive rhabdomyoblastic nature of some primitive tumours, marking with vimentin alone, is discussed.