Leiomyosarcoma of the heart and its pulmonary metastasis, both with prominent osteoclast-like multinucleated giant cells expressing tartrate-resistant acid phosphatase activity.

An autopsy case of cardiac leiomyosarcoma and its pulmonary metastasis, both with osteoclast-like multinucleated giant cells (OMGC) mimicking the so-called giant cell variant of malignant fibrous histiocytoma (MFH), is reported. The patient, a 70-year-old male, was admitted for sudden dyspnea. Extensive work-up established only a left atrial tumor mass. Three months after admission, the patient developed multiple intracranial and pulmonary metastases, followed by a worsening clinical course characterized by semicoma and dyspnea, and subsequently died 6 months after the onset of his symptoms. At subsequent autopsy, the left atrial polypoid tumor was found to have invaded destructively to the left half of the cardiac wall. Histology of the cardiac tumor revealed a bimorphic sarcoma in which a poorly differentiated leiomyosarcoma comfirmed by histologic and immunohistochemical findings was juxtaposed to a small nodule with features closely mimicking giant cell MFH. The pulmonary metastatic nodules exhibited features that were entirely indistinguishable from giant cell MFH except for the fact that a minority of polymorphic cells manifested myogenic differentiation. We believe that such a MFH-like pattern represents a pleomorphic form of leiomyosarcoma rather than a dedifferentiated one. The OMGC within the MFH-like component coexpressed CD68 and tartrate-resistant acid phosphatase activity.