Epithelioid sarcoma: ultrastructural observation of lymphoid cell-induced lysis of tumor cells.

Epithelioid sarcoma of the palm of 7 months' duration was observed in a 30-year-old man. Six months after wide surgical excision there was no evidence of recurrence or metastasis. By light microscopic examination the tumor showed typical nodular arrangement of malignant cells, with necrosis of these cells in the centers of the nodules. Patchy lymphocytic infiltrates were observed at the peripheries of the nodules and also extended in places between the tumor cells. Other types of inflammatory cells were practically absent. By electron microscopic examination it was noted that numerous neoplastic cells formed firm close contacts with lymphocytes. Considerable numbers of neoplastic ells so contacted were damaged or even disintegrated. The damaged tumor cells contained abundant lysosomes. The release of enzymes from these lysosomes in the disintegrating tumor cells might be an important factor underlying the extracellular tissue injury and necrosis so conspicuous in epithelioid sarcoma. The very slow growth of this neoplasm and its slow tendency to metastasize might be related to the high efficacy of lymphocyte-mediated defenses against this tumor.