The biological characteristics of CD 34 + CD 2 + adult acute promyelocytic leukemia and the CD 34 – CD 2

Acute promyelocytic leukemia (APL) is an acute myeloid leukemia characterized by leukemic cells blocked at the promyelocytic stage of granulocytic differentiation. According to the FrenchAmerican-British (FAB) classification, two main cytological subtypes are recognized: (i) classical hypergranular promyelocytic leukemia (M3) and (ii) the microgranular promyelocytic leukemia variant (M3v). Recent results from gene expression profiling suggest that the two morphological subtypes of APL, M3 and M3v, are clearly separable. These studies suggest that the difference may lie in FLT3. This gene has been found to be mutated more frequently in M3v than in M3 APL and more frequently in APL with the short (S-, bcr3) rather than the long (L, bcr1) form of PML/RARα transcript form. Low or negative CD34 expression in addition to absent HLA-DR used to be the paradigm of the APL immunophenotype. However, elevated CD34 expression can occur in APL and appears to be associated with leukocytosis, hypogranular morphology and/or the S-form of the PML/RARα transcript. Similarly, CD2, a T-lineage affiliated antigen, has been associated with M3v morphology and/or the bcr3 isoform. Moreover, a recent study reported that CD34 surface expression is associated with poor clinical outcome in patients with APL. Despite all these data, the issue of CD34 expression in APL remains unsolved because (i) the studies cited above included few APL cases evaluable for CD34 expression; (ii) in the analyzed series the M3 cases have never been distinguished from the M3v ones; (iii) it is still not clear whether CD34 expression identifies a subset of APL-M3 patients with peculiar characteristics. The aim of our study was to make a detailed analysis of CD34 expression at diagnosis in 136 patients with de novo APL in order to determine whether subsets with some discrete biological characteristics could be identified. From the Department of Hematology, University of Bari, Bari, Italy (FA, AM, AP, DP, PC, VL, GS); Section of Hematology, Department of Biomedical Sciences and Advanced Therapies, University of Ferrara, Ferrara, Italy (FL, GLC); Divisione di Ematologia, Azienda Ospedaliera Bianchi-MalacrinoMorelli, Reggio Calabria, Italy (FN, BM); Division of Hematology, Cardarelli Hospital, Naples, Italy (FF).