The value of CD64 expression in distinguishing acute myeloid leukemia with monocytic differentiation from other subtypes of acute myeloid leukemia: a flow cytometric analysis of 64 cases.

CONTEXT Flow cytometric immunophenotyping is a useful ancillary tool in the diagnosis and subclassification of acute myeloid leukemias (AMLs). A recent study concluded that CD64 is sensitive and specific for distinguishing AMLs with a monocytic component (ie, AML M4 and AML M5) from other AML subtypes. However, in that study, the intensity of CD64 was not well defined and the number of non-M4/non-M5 AMLs was small. OBJECTIVE To evaluate the usefulness of CD64 by flow cytometric immunophenotyping in distinguishing AMLs with monocytic differentiation from other AML subtypes. DESIGN Sixty-four AMLs subclassified based on the French-American-British and World Health Organization classifications on pretreatment bone marrows were retrieved from our files (7 M0s, 11 M1s, 17 M2s, 7 M3s, 9 M4s, 7 M5s, 4 M6s, and 2 M7s). A standard panel of markers, including CD2, CD3, CD5, CD7, CD10, CD11b, CD13, CD14, CD15, CD19, CD20, CD33, CD34, CD45, CD56, CD64, CD117, and HLA-DR, were analyzed by flow cytometric immunophenotyping in all AMLs (52 bone marrow samples; 12 peripheral blood samples). RESULTS CD64 was expressed in AML subtypes M0 to M5 in varying intensities: heterogeneously expressed in 1 of 7 M0s; dimly expressed in 3 of 11 M1s; dimly and moderately expressed in 6 and 2 of 17 M2s, respectively; dimly and moderately expressed in 5 and 1 of 7 M3s, respectively; dimly expressed in 4 of 9 M4s; and heterogeneously, moderately, and strongly expressed in 1, 3, and 3 of 7 M5s, respectively. CONCLUSIONS Strong CD64 expression distinguishes AML M5; however, heterogeneous, dim, or moderate expression in itself does not distinguish M0 through M4 subtypes from M5 with dim to moderate CD64 expression. However, any CD64 expression associated with strong CD15 expression distinguishes AML M4 or M5, from other AML subtypes.