The Prevalence of CD56 Expression by Flow Cytometry in Acute Promyelocytic Leukemia Patients Treated with All-Trans Retinoic Acid and Anthracycline Drug Combinations
Horatiu Olteanu, Alexandra M Harrington, Steven H Kroft, Nitin J Karandikar, Franklin F Fuda. Medical College of Wisconsin, Milwaukee, WI; UT Southwestern Medical Center, Dallas, TX
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 (IP) analysis prevented a systematic standardization of flow cytometric (FC) 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 FC in APL patients (pts) by following a rigorously standardized FC protocol, and correlated it with clinicopathologic parameters.
Design: 50 consecutive diagnostic APL bone marrows / peripheral bloods were evaluated by 4-color FC 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 (+) in promyelocytes if >20% cells exceeded a 2% isotype control threshold. CD56 expression status was correlated with clinical and pathologic parameters.
Results: 6/50 (12%) APLs were CD56(+). Comparative clinicopathologic parameters for all APL cases, based on CD56 expression status, are summarized in Table 1. A higher proportion of pts with CD56(+) APL had microganular morphology (p=0.017) and presented with a higher WBC count (p=0.003), as compared to those with CD56(-) APL. There were no other IP differences between the two groups.
Conclusions: 12% of APLs in our series are CD56(+) by FC, 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.
|Age, median (range)||43.5 (20-93)||44.5 (24-88)||0.941|
|WBC, x10e3/ul, median||4.23||80.9||0.003|
|Hemoglobin, g/dL, median||9.7||9.6||0.926|
|Platelets, x10e3/uL, median||27||24||0.315|