The majority of myeloid‐antigen‐positive (My+) childhood B‐cell precursor acute lymphoblastic leukaemias express TEL‐AML1 fusion transcripts

Abstract

The t(12;21) translocation fuses the TEL and AML1 genes and has been found in up to 28% of paediatric B‐cell precursor acute lymphoblastic leukaemias (BCP‐ALL). The AML1 gene is a transcription factor which regulates expression of several myeloid differentiation associated genes. A molecular analysis of TEL‐AML1, E2A‐PBX1, MLL‐AF4, BCR‐ABL expression and an immunophenotypic study of CD13/CD33 myeloid antigen expression have been performed prospectively on tumour cells from 96 paediatric BCP‐ALL patients. Percentages of CD13 or CD33 expressing leukaemic cells were found to be higher in TEL‐AML1 positive cases (n = 22) than in TEL‐AML1 negative (n = 74) cases (P < 0.001). In 22/96 cases (23%) >10% of neoplastic cells were found to express at least one of the two markers. In 14 of these cases (63%), TEL‐AML1 expression was detected, whereas t(4;11), t(11;19) and t(9;22) translocations were found by molecular methods in only three cases (14%). In four cases (18%) no molecular marker was found. These data show that TEL‐AML1 expression is significantly associated with myeloid antigen expression by leukaemic cells and suggests that the prognostic significance of myeloid antigen expression in paediatric ALLs should be re‐evaluated in the light of molecular cytogenetic markers.