Immunophenotyping was performed in 1044 consecutive childhood acute lymphoblastic leukemia (ALL) patients enrolled in the Tokyo Children's Cancer Study Group L04-16 trial, revealing novel findings associated with genetic abnormalities. In addition to TCF3-PBX1 and MEF2D fusions, the CD10(+) subtype of KMT2A-MLLT3-positive ALL frequently exhibited the cytoplasmic-μ(+) pre-B ALL immunophenotype. Although ETV6-RUNX1 was significantly correlated with myeloid antigen expression, more than half of patients expressed neither CD33 nor CD13, while the CD27(+) /CD44(-) immunophenotype was maintained. Expression of CD117 and CD56 in B-cell precursor-ALL was limited to certain subtypes including ETV6-RUNX1 and KMT2A-MLLT3. Besides BCR-ABL1, CRLF2, hyperdiploidy, and hypodiploidy, CD66c was also expressed in Ph-like kinase fusion-, PAX5 fusion-, and DUX4 fusion-positive ALL, but not in MEF2D fusion-positive ALL, indicating constant selectivity of CD66c expression. In T-ALL, SIL-TAL1-positive patients were likely to exhibit a more mature immunophenotype. Expression of CD21 and CD10 was not rare in T-ALL, while lack of CD28 was an additional feature of early T-cell precursor-ALL. Considering the immunophenotype as a prognostic maker, MEF2D fusion-positive ALL with CD5 expression may be associated with a poorer prognosis in comparison with those lacking CD5 expression. In cases with characteristic marker expression, the presence of certain fusion transcripts could be predicted accurately.
Keywords: acute lymphoblastic leukemia; flow cytometry; genetic mutations; immunophenotype; novel fusion genes.
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