The Incidence of CD56 Expression by Flow Cytometry in Acute Promyelocytic Leukemia in Patients Treated With All-Trans Retinoic Acid and Anthracycline Drug Combinations
Authors: Horatiu Olteanu, MD, PhD | Alexandra M. Harrington MD | Steven H. Kroft, MD
Department of Pathology, Medical College of Wisconsin, Milwaukee, WI
N.J. Karandikar, MD, PhD | F.F. Fuda, DO
UT Southwestern Medical Center, Dallas, TX
Recent cooperative studies have linked CD56 positivity in acute promyelocytic leukemia (APL) with an increased risk of relapse, and with the presence of immaturity-associated and T-cell antigens on leukemic promyelocytes. The drawbacks of these multicenter studies are twofold: lack of centralized immunophenotypic analysis prevented a systematic standardization of flow cytometric results, and a possible selection bias resulting from not all centers assessing for CD56 expression. Because of these confounding factors, we studied the expression of CD56 by flow cytometry in APL with a rigorously standardized flow cytometric protocol, and correlated it with clinicopathologic parameters.
64 consecutive diagnostic APL bone marrows or peripheral bloods were evaluated by 4-color flow cytometry and cluster analysis, with antibodies against CD2, CD3, CD4, CD5, CD7, CD8, CD10, CD11b, CD13, CD15, CD16, CD19, CD20, CD33, CD34, CD38, CD45, CD56, CD79a, CD117, HLA-DR, MPO, and Tdt. An antigen was considered positive in promyelocytes if >20% cells exceeded a 2% isotype control threshold. CD56 expression status was correlated with clinical and pathologic parameters. Results: 7/64 APLs (11%) were CD56(+). Comparative clinicopathologic parameters for all APL cases, based on CD56 expression status, included age, gender, morphology (microgranular vs. granular), CBC data, cytogenetic and molecular findings. A higher proportion of patients with CD56(+) APL had microgranular morphology (p=0.027), and they presented with a higher WBC count (p=0.003), as compared to those with CD56(-) APL. There were no other immunophenotypic differences between the two groups.
11% of APLs in our series are CD56(+) by flow cytometry, which is comparable to data reported in the literature (11-15%). CD56 expression correlated with microgranular morphology and high WBC count, as shown by other authors. In contrast to a recent study, there was no association of CD56 expression with CD2, CD7, CD15, CD34, CD117, or HLA-DR positivity.
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