Report of a case with chronic myelomonocytic leukemia: demonstration of leukemic monocytes lacking nonspecific esterase by flow cytometry using monoclonal antibodies.

: Chronic myelomonocytic leukemia (CMML) is a rare leukemia, which is now included in myelodysplastic syndromes. In a small number of patients with CMML, problems in the diagnosis have been reported, especially when atypical morphological features in both monocytic and granulocytic cells due to dysmyelopoiesis are prominent, or when cytochemical characteristics are lost in the leukemic cells. The case history of a sixty-seven year-old male patient with CMML is described. The diagnosis of CMML in the patient was supported by the following evidence: chronic course of his disease; increased monocyte-like cells without other cause; normocytic anemia; immature granulocytic cells with hypogranular feature and giant platelets were observed in the peripheral blood. The bone marrow showed myeloid hyperplasia. Serum muramidase and vitamin B12 levels were increased, while neutrophil alkaline phosphatase score was low in the peripheral blood. Ph' chromosome was negative. The monocyte-like cells completely lacked nonspecific esterase. However the cells were confirmed as monocytic cells by flow cytometry using monoclonal antibodies to monocytes (OKM5).