Acute Monocytic Leukemia Diagnosed By Flow Cytometry Includes Acute Myeloid Leukemias With Weakly Or Faintly Positive Non-Specific Esterase Staining

A diagnosis of acute monocytic leukemia (AML-M5) based on alpha-naphthyl butyrate esterase (alpha-NB) staining has some problems, because AML-M5 leukemic cells often show weak or faint positivity on alpha-NB staining. In these situations, some cases of AML-M5 tend to be misdiagnosed as AML-M0. Therefore, we evaluated the significance of weak or faint alpha-NB staining in AML-M5 diagnosed by flow cytometry (FCM). Nineteen AML cases in which leukemic cells were negative for naphthol AS-D chloroacetate esterase staining were studied. For FCM, we defined leukemic cells as having a monocytic nature when more than 10% of the leukemic cells were positive for at least one of the following antigens: CD4, CD11c, CD14, and CD64. The monocytic nature determined by FCM was consistent with positive or weak positivity on alpha-NB staining. Five of 6 cases in which leukemic cells exhibited faint positivity for alpha-NB staining could be diagnosed as AML-M5 by FCM, while negative alpha-NB staining was consistent with a diagnosis of AML-M0. These results suggest that AML-M5 should be taken into consideration even when leukemic cells are faintly positive for alpha-NB staining.