Smooth and skeletal muscle myosins in spindle cell tumors of soft tissue. An immunohistochemical study.

Histological localization of myosins of the smooth and skeletal muscles was investigated in comparison with that of myoglobin by immunoperoxidase technique using the antibody against each of them in surgical specimens from spindle cell tumors and tumor-like lesions of the soft tissue. Skeletal muscle myosin was demonstrated in all of the cases of rhabdomyosarcoma, whereas myoglobin was found in 75% of the examined cases. Smooth muscle myosin was widely distributed not only in the tumor cells of smooth muscle origin such as leiomyosarcoma and angioleiomyoma, but also in the tumor cells showing myofibroblastic differentiation such as malignant fibrous histiocytoma and in the epithelial components of synovial sarcoma. The results showed that skeletal muscle myosin can be regarded as an excellent marker in the diagnosis of rhabdomyosarcoma and that smooth muscle myosin is a useful marker of leiomyosarcoma and leiomyomas, and of tumors with myofibroblastic differentiation.