Malignant lymphoma of true histiocytic origin: Histiocytic Sarcoma

Summary Ten tumors of true histiocytic origin (Histiocytic Sarcoma) are presented. The tumor cells were identified as histiocytes by immunological, cytochemical and ultrastructural criteria (cytoplasmic lysozyme activity, presence of C3 and Fe receptor, strong acid phosphatase and alpha-naphtyl acetate esterase activity, presence of lysosomes, absence of cell junctions and evidence of phagocytosis). The tumors identified in this way showed the following histological characteristics: diffuse proliferation of large tumor cells with ample cytoplasm, containing granular or occasionally diffuse diastase resistent PAS positive material, erythrophagocytosis, and haemosiderin pigment. The large or enormous nuclei were irregular, with occasional deep indentations, sharply defined nuclear membrane, coarse chromatin and conspicuous nucleoli. Despite the uniformity of these criteria differences in presence of alpha₁-antitrypsin, alpha₁-antichymotrypsin and 5 Nucleotidase activity and the number of lysosomes in the cytoplasm were found. The findings are suggestive of a spectrum of cytological changes in these Histiocytic Sarcomas.The clinical picture ranged from monolocalization in a lymphoid organ to that of a diffuse Malignant Histiocytosis. The relationship between good response to therapy and complete remission and the absence of alpha₁-antitrypsin and a high number of lysosomes is discussed.