Table 6.

T-ALL Diagnostic Considerations and Ancillary Testing.

Clinical Information	History of CML: consider T-lymphoblastic transformation (rare) Eosinophilia: consider “myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions,” including FGFR1-r and FLT3-r
Immunophenot yping	Flow cytometry	ETP ALL, NOS and ETP ALL, BCL11B-a: cytoplasmic CD3+*, CD7 +, CD8−, CD1a−, one or more myeloid/stem cell markers (CD34, CD117, HLA-DR, CD13, CD3, CD11b, CD65), CD4+/−, CD2+/−, CD5 (<75% of blasts) “Near-ETP T-ALL.”: ETP immunophenotype with ≥75% of blasts CD5+ *T-ALL characteristically expresses cCD3, but a specific level of expression is not required for a diagnosis of T-ALL Note: Dedicated flow cytometry studies to characterize the neoplastic cells for later MRD monitoring is strongly recommended at diagnosis; however, MRD studies utilize a limited panel of antibodies and do not provide comprehensive immunophenotypic analysis of the blasts.
	Immunohistochemis try	BCL11B: Positive in a subset of ETP ALL, BCL11B-a; negative in T-ALL with TXL3::BCL11B (TXL3-r) LMO2: Possible role for immunohistochemistry in the detection of T-ALLwith LMO2-r PU.1: needs validation but might be useful for TALL with SPI1-r
Cytogenetics	Fluorescence in situ hybridization (FISH)	BCL11B breakapart: ETP-ALL with BCL11B-a (subset) Note: FISH studies will not identify BCL11B-r alterations from enhancer amplification downstream of BCL11B that results in looping of the enhancer to BCL11B
Molecular Diagnostics	Clonality studies	Recommended at diagnosis to facilitate molecular MRD monitoring *The presence or absence of a TCR and/or IGH clone cannot utilized for lineage assignment (T-ALL versus B-ALL).

New/provisional Entities in the ICC subclassification are underlined.