A light and electron microscopic study with comments on their relation to malignant fibrous histiocytoma and angiosarcoma.

Analysis of 365 cases of malignant soft tissue tumors revealed 83 cases of liposarcoma. The ages of the patients were distributed between 18 and 86 years with a mean average of 54.3 years. Approximately 50% of the cases were located in the lower extremity. Histologically, they consisted of 5 types; well differentiated (17 cases), myxoid (49 cases), round cell (3 cases), pleomorphic (11 cases), and mixed (3 cases). The appearance of lipoblasts of either the signet-ring type or mulberry (multivacuolated) type with displaced nuclei was the common characteristic feature for all types. Electron microscopically, lipid droplets were found inside of endoplasmic reticulum in lipoblasts, and abundant glycogen granules were seen in the cells containing only few lipid droplets. The lipoblasts were usually located close to the vascular wall in the interstitium, and findings suggesting an intimate relation between pericytes and lipoblasts were encountered. Although the differential diagnosis of malignant fibrous histiocytoma and liposarcoma was made possible by the appearance of lipoblasts in the latter, storiform pattern and histiocyte-like cells sometimes appeared in poorly differentiated liposarcoma. This tendency was also found in angiosarcoma. A close follow-up of recurrent cases revealed that there are actually cases of liposarcoma with malignant fibrous histiocytoma-like pattern and angiosarcoma with malignant fibrous histiocytoma-like pattern. It was considered that malignant fibrous histiocytoma-like figures can appear in various poorly differentiated sarcomas.