Immunophenotypic Pattern of Myeloid Populations by Flow Cytometry Analysis

We present our experience with immunophenotypic characteristics of benign and malignant myeloid populations, with emphasis on differential diagnosis especially between eosinophils, dysplastic granulocytes, neoplastic promyelocytes, and monocytes. Eosinophils are characterized by bright CD45, high side scatter (SSC), very low forward scatter (FSC), positive CD11b, CD11c, CD13, CD15, and CD33. They are negative for CD10, CD14, CD16, CD56, CD64, and HLA-DR. Mature monocytes are positive for CD11b, CD11c, CD13, CD14, CD33, and CD64, and may express CD2 and CD4. Blasts in acute myeloid leukemias (AML) with minimal differentiation have low SSC and moderate CD45 expression and are positive for CD34, CD117, CD13, HLA-DR, and CD33 and may be positive for TdT, CD4, and CD11c. In acute promyelocytic leukemia (APL), four FC patterns can be recognized. The majority of cases represented classical (hypergranular) APL and were characterized by high SSC, positive CD117, usually negative CD34, heterogeneous CD13, and bright CD33 (pattern 1). The second most common type, corresponding to hypogranular (microgranular) variant of APL, differed from classical APL by low SSC and frequent coexpression of CD2 and CD34 (pattern 2). Rare cases of APL (pattern3) showed mixture of neoplastic cells (SSClow/CD2+/CD13+/CD33+/CD34+/CD117+) and prominent population of benign granulocytes/maturing myeloid precursors (SSChigh/CD10+/−/CD16+/(/CD117(). One case showed two APL populations, one with hypogranular and one with hypergranular characteristics (pattern 4). Detailed phenotypic characteristics of neoplastic monocytes and dysplastic granulocytes with their differential diagnosis are also presented.