The spectrum of Leu-M1 staining in lymphoid and hematopoietic proliferations.

Leu-M1, or MMA, originally was proposed as a differentiation antigen on myelomonocytic cells and was said to be useful as an aid in distinguishing lymphoid from myeloid leukemias. Subsequently, it was proposed by Hsu and Jaffe as a useful marker of Reed-Sternberg cells and their variants in paraffin-embedded sections in Hodgkin's disease and as an aid in the differential diagnosis among Hodgkin's disease, non-Hodgkin's lymphomas, and reactive lymphoid proliferations. In order to test the usefulness of this antibody in classifying acute leukemias and to investigate the spectrum of its positivity on B5 and/or formalin-fixed, paraffin-embedded tissue sections, a variety of benign and neoplastic hematopoietic and lymphoid disorders were studied, using Leu-M1 and the ABC immunoperoxidase technic. Definite positivity in neoplastic cells was present in 4 of 16 patients with acute nonlymphocytic leukemias, 0 of 9 patients with acute lymphocytic leukemias/lymphoblastic lymphoma, 11 of 13 patients with Hodgkin's disease, and 0 of 18 patients with non-Hodgkin's lymphomas. Granulocyte staining could be identified in many cases. Although not identified in tonsillar sections from three patients, variable numbers of sometimes large mononuclear and rare binucleate cells were identified in some of the 14 reactive lymph nodes studied as well. These data, together with other data recently reported, suggest that in routinely processed tissue sections, Leu-M1 is a relatively sensitive marker for Hodgkin's disease, but it does not appear to be specific for that diagnosis. Although marking some acute nonlymphocytic leukemias in tissue sections, its lack of sensitivity and possible lack of specificity severely limits its usefulness in classifying the acute leukemias.