Malignant fibrous histiocytoma. Cytologic, light microscopic and ultrastructural studies

Studies of the cytologic, light-microscopic and electron-microscopic features of three malignant fibrous histiocytomas (MFH) confirmed the presence of histiocytelike and fibroblastlike cells. The ultrastructural features suggest that the neoplasm possibly originates in undifferentiated mesenchymal cells that are capable of differentiating into histiocytic and fibroblastic cells. Cytologic features seen in smears obtained by thin needle aspiration included loose aggregates of markedly pleomorphic, elongated cells, histiocytelike cells and isolated bizarre giant cells. Phosphotungstic acid hematoxylin (PTAH) and oil red O staining of air-dried smears were helpful in differentiating MFH from pleomorphic variants of liposarcoma and rhabdomyosarcoma.