Primary bone sarcoma with rhabdomyosarcomatous component.

We present three cases of primary bone sarcoma with rhabdomyosarcomatous component which in one case appeared in a pure form, i.e., as rhabdomyosarcoma; in the other two cases it presented as one of multiple components of the tumor. The first patient was a 70-year-old man with a tumor of the left femur involving surrounding soft tissue of the thigh. Histologically, this was a case of so-called dedifferentiated chondrosarcoma with pleomorphic rhabdomyosarcoma representing high grade malignant component. The second patient, a 31-year-old man, developed a tumor in the left tibia which was a rare, fibrosarcoma-like type of rhabdomyosarcoma. The third patient was a 43-year-old woman with a tumor in the left tenth rib which was shown to be osteo- and chondrosarcoma with a minor rhabdomyosarcomatous component and was classified as malignant mesenchymoma. All patients were treated by surgery and chemotherapy. The first two of them died of metastatic disease 3 months, and 3 years and 4 months following surgery, respectively. Light microscopical diagnosis of rhabdomyosarcoma of hematoxylin-eosin sections was confirmed immunohistochemically in each case using reactions to desmin, muscle specific actin and myoglobin, and ultrastructurally in two cases. Rhabdomyosarcomatous component in primary bone tumors appears to be rarely present but more cases may be diagnosed in the future, if immunohistochemical and ultrastructural examinations are to be employed.