Intermediate filaments in eosinophilic cells of epithelioid sarcoma: a light-microscopic, ultrastructural, and...

A 41-year-old woman had a mass in her thigh for 5 months. The neoplasm had areas histologically typical of epithelioid sarcoma, but there were also cells with abundant eosinophilic, vacuolated cytoplasm and peripheral, distorted nuclei. These cells resembled signet-ring cells but contained no intracellular mucin. Rather, their cytoplasm was filled with large aggregates of 7-10 nm diameter, nonperiodic filaments, and lipid droplets. Lipid droplets and filaments are common in epithelioid sarcomas, but their presence in sufficient volume to displace the nucleus in a signet-ring fashion has not been described. Electrophoretic analysis of a tumor extract showed that actin was present in insufficient concentration (1-3%) to account for the filamentous aggregates. However, two proteins of 51,000 and 63,000 daltons apparent molecular weight comprised 40-50% of the total protein, suggesting that one or both were the major subunits of the abundant cytoplasmic filaments. Filaments of identical ultrastructural size have been described in a variety of human neoplasms and may be related to a filament characterized in other species and termed vimentin.