THE MAJORITY OF MYELOID-ANTIGEN-POSITIVE (MY(-CELL PRECURSOR ACUTE LYMPHOBLASTIC LEUKEMIAS EXPRESS TEL-AML1 FUSION TRANSCRIPTS()) CHILDHOODB)

The t(12;21) translocation fuses the TEL and AML1 genes and has been f ound in up to 28% of paediatric B-cell precursor acute lymphoblastic l eukaemias (BCP-ALL). The AML1 gene is a transcription factor which reg ulates expression of several myeloid differentiation associated genes. A molecular analysis of TEL-AML1, E2A-PBX1, MLL-AF4, BCR-ABL expressi on and an immunophenotypic study of CD13/CD33 myeloid antigen expressi on have been performed prospectively on tumour cells from 96 paediatri c BCP-ALL patients. Percentages of CD13 or CD33 expressing leukaemic c ells 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% o f neoplastic cells were found to express at least one of the two marke rs. In 14 of these cases (63%), TEL-AML1 expression was detected, wher eas t(4;11), t(11;19) and t(9;22) translocations were found by molecul ar methods in only three cases (14%). In four cases (18%) no molecular marker was found. These data show that TEL-AML1 expression is signifi cantly associated with myeloid antigen expression by leukaemic cells a nd suggests that the prognostic significance of myeloid antigen expres sion in paediatric Ws should be re-evaluated in the light of molecular cytogenetic markers.