MPO and acute myeloid leukemia: Flow cytometry analysis of the peripheral blood revealed an aberrant blast population, which accounted for 94% of total analyzed cells and co-expressed CD13 (small subset), CD33, CD123, HLA-DR, CD64, CD11b (subset), CD15 (subset), CD38, and cytoplasmic myeloperoxidase (MPO), while being negative for CD34 and all other markers tested (Figure 1B), consistent with a diagnosis of AML.