Myosin and myoglobin as tumor markers in the diagnosis of rhabdomyosarcoma. A comparative study.

Antibodies against the myosin heavy chain of adult chicken pectoral muscle and heart muscle which cross-react with myosin of human fast type II fibers ( antifast myosin) and slow type I fibers ( antislow myosin), respectively, and antibodies against human myoglobin have been assessed for their usefulness in diagnosing rhabdomyosarcoma. Formaldehyde-fixed and paraffin-embedded tissue and the avidin-biotinyl-peroxidase complex technique were used. Of 23 rhabdomyosarcomas studied, 20 were positive with antifast myosin and 11 with antimyoglobin . All tumors were negative with antislow myosin. Positive staining was observed in all three types of rhabdomyosarcoma, i.e., embryonal, alveolar, and pleomorphic, regardless of the antiserum used. Staining with antimyoglobin was generally limited to the cytoplasm-rich tumor cells. Besides rhabdomyosarcomas, the only other positive neoplasms were those which contained rhabdomyoblastic differentiation such as malignant Triton tumors and malignant mixed müllerian tumors. Our results indicate that antibodies against the fast myosin heavy chain are a useful tool for diagnosing rhabdomyosarcoma and that they can be used to distinguish that tumor from other small round cell tumors in childhood. The results are discussed in the light of the embryogenesis of skeletal muscle.