Interdigitating reticulum cells (IRC) are dendritic, nonphagocytic histiocytes found in thymus-dependent areas of lymphoid tissues. We report two cases of large cell lymphoma having features of IRC in patients 13 and 17 years old. In each case the diagnosis was suggested by light and electron microscopic features, positive immunoperoxidase staining for S-100 protein, and additional immunoperoxidase findings. Both patients presented with aggressive lymphomas and were treated with intensive combination chemotherapy. Each patient achieved a complete clinical remission, then rapidly relapsed and died with disseminated disease 3 and 9 months after presentation. Novel findings included strong staining of specimens with an antibody to epithelial membrane antigen, staining of one specimen with peanut agglutinin in the pattern previously described in normal IRC, and a DNA content analysis that showed aneuploid stem cell lines in both patients.

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