Microgranular and t(11;17)/PLZF-RARa Variants of Acute Promyelocytic Leukemia Also Present the Flow Cytometric Pattern of CD13, CD34, and CD15 Expression Characteristic of PML-RARa Gene Rearrangement

Acute promyelocytic leukemia (APL) is a subtype acutemyeloid leukemia inwhich leukemic promyelocytes predominate in the bone marrow (BM). Rapid diagnosis is critical for treatment decision since all-trans-retinoic acid must be administrated promptly. The microgranular variant may be of difficult diagnosis, as it may be confused with other diseases on morphological grounds. The purpose of this study was to determine if the microgranular variant has the same antigenic profile as the classical hypergranular type. The immunophenotype of leukemic cells from the bone marrow of 50 patients, with the PML-RARa gene rearrangement confirmed by RT-PCR, was determined by flow cytometry using a large panel of 22 monoclonal antibodies and a polyclonal anti-TdT antibody. Thirty-four cases were classified as classical APL and 16 as microgranular APL. The immunophenotypic profile of the two subtypes was indistinguishable concerning the presence or absence of these antigens, including the absence of reactivity for the HLA-DR antigen. The simultaneous immunophenotypic combination of a unique major cell population, heterogeneous intensity of expression of CD13, and the typical pattern of CD15/CD34 expression were similarly present in the hypergranular and microgranular subtypes. Homogeneous expression of CD33 was observed in 76% of the classical APL cases and in 100% of the microgranular cases. Additionally, we have studied two cases of PLZF-RARa APL that also displayed the same immunophenotype described for classical APL. Thus, the immunophenotypic profile highly characteristic of the PML-RARa gene rearrangement was also observed in microgranular and PLZF-RARa variants of APL. Am. J. Hematol. 76:44–51, 2004. a 2004 Wiley-Liss, Inc.