CD56 expression in myeloperoxidase-negative FAB M5 acute myeloid leukemia

CD56 is a natural killer (NK) cell marker that has been identified in approximately 15-20% of acute myeloid leukemia (AML) cases, where it has been associated with monocytic morphology and chromosomal abnormalities such as trisomy 8, t(8;21), t (15;17), and 11q23 rearrangements. The clinical presentation, chromosomal abnormalities as detected by fluorescent in-situ hybridization (FISH), and clinical outcomes of 7 patients with AML are presented. These cases were characterized by French-American-British (FAB) M5 morphology, myeloperoxidase (MPO) negativity, and co-expression of myelomonocytic and NK cell-associated antigens (CD11c+, CD13+, CD15+, CD33+, HLA-DR+, and CD56+). All patients presented lymph node, hepatic, or splenic involvement at diagnosis. Despite the homogeneous morphologic and immunophenotypic characteristics the outcomes varied considerably. Two patients died during induction therapy, but the other five patients attained complete remission (CR). Of these five patients, 4 have received a bone marrow transplantation (autologous or allogeneic) and 3 of them are in CR (median follow-up: 45 months). The three patients with 11q23 rearrangements had a poor outcome and died of their disease within 1 year of diagnosis. Further studies with a larger group of patients would help establish the actual prognostic value of these morphologic, immunophenotypic and cytogenetic features.