Utility of CD117 Expression in the Diagnosis of T/Myeloid Mixed Phenotype Acute Leukemia.
Jason S Willis, Jacqueline Emmons, Nitin J Karandikar, Franklin S Fuda. University of Texas Southwestern Medical School, Dallas
Background: Acute myeloid leukemias commonly express CD117. However, the utility of this marker in the diagnosis of other acute leukemias is incompletely evaluated, particularly in the context of mixed phenotype leukemias, where myeloperoxidase (MPO) expression has assumed paramount importance without clarification of technique/cutoffs. In this study, we evaluated CD117 and MPO expression by flow cytometry on acute myeloid leukemia (AML), B lymphoblastic leukemia (BLL), T lymphoblastic leukemia (TLL), mixed phenotype acute leukemia, B/myeloid (MP-B/M), and mixed phenotype acute leukemia, T/myeloid (TP-T/M).
Design: A search of our clinical flow cytometry database was performed for initial diagnostic cases of AML, BLL, TLL, MP-B/M, and MP-T/M. Mixed phenotype leukemias were defined by either the 2001 or 2008 WHO criteria. Positivity for MPO and CD117 was defined by at least a 20% threshold based on isotypic controls.
Results: In 55 cases of newly diagnosed AML, 50 (91%) were CD117+ and 29 (53%) were MPO+ (25 [45%] MPO+/CD117+, 4 [7%] MPO+/CD117-, 25 [45%] MPO-/CD117+, 1 [2%] MPO-/CD117-). In 19 cases of MP-T/M (11 by 2001 WHO criteria, 8 by 2008 WHO criteria), 17 cases (89.5%) were CD117+, with the breakdown showing CD117+ in 10/11 (90.9%) of 2001 WHO cases and 7/8 (87.5%) of 2008 WHO cases (7 [37%] MPO+/CD117+, 1 [5%] MPO+/CD117-, 10 [53%] MPO-/CD117+, 1 [5%] MPO-/CD117-). In 27 cases of TLL, 4 cases (14.8%) were CD117+. In 47 cases of MP-B/M (20 by 2001 WHO criteria, 27 by 2008 WHO criteria), 14 cases (30%) were positive for CD117, with the breakdown showing CD117+ in 8/20 (40%) of 2001 WHO cases and 6/27 (22%) of 2008 WHO cases (6 [13%] MPO+/CD117+, 21 [45%] MPO+/CD117-, 8 [17%] MPO-/CD117+, 12 [25%] MPO-/CD117-). In 49 cases of BLL, 2 cases (4%) were CD117+.
Conclusions: Mixed Phenotype Acute Leukemia, T/Myeloid expresses CD117 with the same frequency as AML. CD117 expression is uncommon in TLL and MP-B/M and is exceedingly rare in BLL. Thus, the detection of CD117 should trigger careful evaluation for MPO expression. The concordance between CD117 and MPO expression in this entity is also similar to that seen in AML, raising the possibility of using CD117 and other myeloid markers as surrogate markers for MPO, especially with the undefined cutoffs and criteria for designating a tumor MPO+. The near ubiquitous expression of CD117 in MP-T/M may suggest a common genetic basis that needs further elucidation.
Monday, February 28, 2011 1:00 PM
Poster Session II # 191, Monday Afternoon