[1287] T-Cell-Associated Fluorescence In Situ Hybridization (FISH) Probes May Help Distinguish between T Lymphoblastic Leukemia (T-LBL) and Acute Myeloid Leukemia with T-Cell Antigen Expression (AML-T)

DS Bosler, CA Hanson, RA Knudson, RP Ketterling, JD Hoyer. Cleveland Clinic, Cleveland, OH; Mayo Clinic, Rochester, MN

Background: The diagnostic distinction between T-LBL and AML can be challenging, as co-expression of both myeloid and T-cell associated antigens can be found in both leukemias. Our study evaluated the potential diagnostic role of various T-cell-associated FISH probes in the evaluation and classification of T-LBLs and AMLs.
Design: We identified 145 acute leukemias (75 T-LBL, 70 AML) with diagnostic flow cytometry and available cell pellets for FISH studies. 28 of 75 T-LBLs had at least one myeloid antigen expressed. AMLs selected were either "with minimal differentiation" or "without maturation"; 43 of 70 AMLs had expression of T-cell associated antigen(s). FISH probes used included: SIL/TAL1 (1p32), HOX11L2/BCL11B, t(5;14)(q35;q32), and also break apart probes for T-cell receptor α/δ(TCR-AD) (14q11.2), and T-cell receptor β (TCR-B) (7q34). Histograms (for T-LBL and AML-T) and cytogenetic karyotypes were reviewed when available.
Results: At least one FISH abnormality was identified in 35 (47%) of 75 T-LBLs. A TCR-AD split was the most frequent abnormality detected (19/75, 25%), and 5/75 (7%) T-LBLs had more than one abnormality identified by FISH. There were no reliable differences in the abnormalities detected by FISH in the T-LBLs that had myeloid antigens expressed versus those that did not. No T-cell FISH abnormalities were identified in any of the 70 AML cases, regardless of T-cell antigen expression.

	% Any FISH Abnl	% >1 FISH Abnl	% TCRAD	% TCRB	% SIL/TAL	% HOX11L2/ BCL11B
T-LBL (n=75)	47	7	25	9	12	7
AML-T (n=43)	0	0	0	0	0	0
AML (n=27)	0	0	0	0	0	0

In 67 T-LBL cases with both FISH and karyotypes available, 25/39 (64%) of the FISH abnormalities detected were not identified by karyotype analysis.
Conclusions: A FISH panel directed at four loci associated with T-LBL (SIL/TAL, HOX11L2/BCL11B, TCR-AD and TCR-B) identified abnormalities in 47% of T-LBL cases but found none in AMLs with minimal differentiation or without maturation. Importantly, no T-cell associated FISH abnormality was identified in any of the 43 AMLs with T-cell associated antigens. Thus, the use of this limited FISH panel in cases of acute leukemia with both T-cell and myeloid antigen expression may help in the classification of these challenging cases.
Category: Hematopathology

Tuesday, March 23, 2010 11:00 AM

Platform Session: Section B, Tuesday Morning