Ultrastructural observation of epithelioid sarcoma

Epithelioid sarcoma located in the right hip-to-thigh region of a 58-year-old female was studied by light microscopy, immunohistochemistry, and electron microscopy. Light microscopy revealed both light and dark cells among the tumor cells. Round, homogeneous, eosinophilic bodies were noted extracellularly and intracellularly. Extracellular bodies were similar in size to tumor cells and were not stained by PAS or Congo red. In contrast, intercellular bodies were PAS positive and diastase resistant. Tumor cells were positive for vimentin, keratin, and, partially, for epithelial membrane antigen. Ultrastructurally, tumor cells had numerous microfilaments with tonofibril-like arrangement, lipid droplets, and reticulogranular structure in their cytoplasm. The reticulogranular structure was similar to the tonofilaments recognized in degenerative tumor cells. Oval filamentous bodies were recognized in the stroma. They appeared to be very similar to colloid bodies derived from tonofilaments of keratinocytes. It was considered that the filamentous bodies corresponded to extracellular eosinophilic bodies and showed signs of fibrous necrosis of tumor cells. Intracellular eosinophilic bodies were considered to be lipid droplets.