TRUE HISTIOCYTIC LYMPHOMA - A STUDY OF 12 CASES BASED ON CURRENT DEFINITION

True histiocytic lymphoma (THL), as it is currently defined, is a rare entity. We report 12 cases of THL seen at Stanford over the last ten years. By definition, the neoplastic cells in each case showed histolo gical and immunological evidence of histiocytic differentiation. Seven females and five males ranged in age from 9 to 67 years. Sites of inv olvement included lymph node, soft tissue, bone, stomach, small intest ine, mediastinum, kidney, breast and salivary gland. Lymph nodes showe d diffuse architectural effacement and/or a paracortical pattern of in volvement. The infiltrates involved other tissues in a diffuse pattern . Cytologically the cells were characterized by abundant eosinophilic cytoplasm and enlarged, indented eccentrically placed nuclei containin g prominent nucleoli. In all cases the cytological features were suffi ciently atypical to indicate a neoplastic infiltrate, Paraffin section immunophenotyping demonstrated reactivity of the atypical cells for C D15, 43, 45RO, 45RB, 68, lysozyme and/or S100. In frozen sections, the atypical cells demonstrated reactivity for CD4 (cytoplasmic), 11c, 14 , 15, and/or 68, Genotypic studies were performed on 3 cases, one of w hich showed rearrangements of immunoglobulin heavy and light chain gen es. Follow-up was available on eleven patients, six of whom died of di sease 0.5 to 36 months following diagnosis.