The Incidence of CD56 Expression by Flow Cytometry in Acute Promyelocytic Leukemia in Patients Treated With All-Trans Retinoic Acid and Anthracycline Drug Combinations

The Incidence of CD56 Expression by Flow Cytometry in Acute Promyelocytic Leukemia in Patients Treated With All-Trans Retinoic Acid and Anthracycline Drug Combinations

October 1, 2012  |  Research

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

Abstract

Background

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.

Design

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.

Conclusion

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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