Sarcoma arising from interdigitating cells. Cytology and cytochemistry.

The cytologic features of a highly malignant sarcomatous tumor in a 37-year-old male, arising from interdigitating cells and localized in the mediastinum, lymph nodes and skin, are described. Cytologically this sarcoma was characterized by large cells with ill-defined, faintly basophilic cytoplasm, monocytoid or multilobulated nuclei and a reticular chromatin structure; very prominent nucleoli were seen in some of the cells. Some of the tumor cells were spindle shaped. The ultrastructurally characteristic invaginations of the cell membrane were not obvious in the cytologic smear, although the nuclear membrane showed deep, narrow, channel-like indentations. The specific ultrastructural, immunologic and cytochemical characteristics of the interdigitating cells were recognized in the tumor cells. Adenosine triphosphatase was present in the tumor cells in large amounts, while acid phosphatase, acid alpha-naphthyl acetate esterase and other enzymes were absent. The described tumor must be considered another tumor of the mononuclear phagocyte system; the proposed name is "interdigitating-cell sarcoma."