We studied a case of epithelioid sarcoma that had developed on the right sole of a 27-year-old Japanese man. The lesion, which had a history of 6 months, presented as indurated erythematous plaque of 4 × 7 cm scattered with several irregular scars. Microscopically, the majority of the proliferated tumor cells were large, plump epithelioid-like cells with eosinophilic cytoplasm and an oval nucleus. The remainder were fibroblast-like, bearing spindle-shaped cell bodies. Immunohistochemistry indicated that the epithelioid-like cells were positive for Vimentin and AE1/AE3, but that the fibroblast-like cells were negative. Electron microscopy revealed that the former cells were characterized by an abundant and monotonous cytoplasm being filled with intermediate filaments densely arranged throughout the cell bodies. Small mitochondria were the only organelles around the nucleus. On the other hand, the fibroblast-like cells were characterized by prominent cytoplasmic organelles, including mitochondria, rough endoplasmic reticulum, Golgi apparatus and free ribosomes, and by abundant glycogen within the cytoplasm. Regardless of such different features, both cells were partially surrounded by basal lamina and exhibited close contact with juxta cells with gap junctions. These findings support the belief that the tumor was related etiologically to synovial sarcoma.
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