ATYPICAL TUMOR OF THE MEDIASTINUM - EPITHELIOID HEMANGIOENDOTHELIOMA CONTAINING METAPLASTIC BONE AND OSTEOCLAST-LIKE GIANT-CELLS

A 66-year-old woman presented with a superior-anterior mediastinal mass that contained considerable calcification by computed tomography. Initial biopsy interpretation was inconclusive but suggested a giant cell sarcoma of soft parts because the tumor contained atypical epithelioid cells and osteoclastlike giant cells. After radiation and chemotherapy, the tumor was removed. It contained large epithelioid cells, pale chondroid areas, metaplastic bone, and osteoclastlike giant cells. Immunohistochemical and electron microscopic studies revealed the epithelioid cells to be factor VIII positive and to contain abundant intermediate filaments, micropinocytotic vesicles, Weibel-Palade bodies, basal lamina, and primitive cell-cell junctions. These epithelioid cells also stained for muscle-specific actin (HHF-35), yet were negative for desmin and cytokeratins (CA M 5.2 and AE1/3). The findings were most consistent with those reported to occur in epithelioid hemangioendothelioma.