Expression of TEL-AML1 fusion transcripts and response to induction therapy in standard risk acute lymphoblastic leukemia

We prospectively examined the frequency of the t(12;21)TEL-AML1 fusion in 5 04 children with newly diagnosed standard risk ALL using RT-PCR assays. Cel ls from 95 patients (18.8%) were TEL-AML1(+). There was a significantly hig her frequency of pseudodiploidy among the TEL-AML1(+) cases (39.4% versus 1 4.1%, P=0.001), primarily because structural abnormalities involving 12p an d del(6q) occurred more frequently in the TEL-AML1(+) group. TEL-AML1(+) AL L was more sensitive to the induction chemotherapy than TEL-AML1(-) ALL. Th e percentage of "rapid early responders", i.e., patients who achieved an M1 (<5% blasts) or M2 (5-25% blasts) marrow status on day 7 of induction chem otherapy, was significantly higher among TEL-AML1(+) cases. The quality of remission of RT-PCR positive cases was excellent, as evidenced by the very low to absent MRD burden of their end-of-induction bone marrow specimens. T EL-AML1(+) patients also had an excellent early EFS outcome. The probabilit y of EFS at 30 months from study entry were 98.9 +/- 1.0% for the TEL-AML1( +) group and 92.1 +/- 1.5% for the TEL-AML1(-) group (P=0.0001). This prosp ective study significantly expands the knowledge gained from previous studi es regarding the prognostic significance of t(12;21)TEL-AML1 fusion in pedi atric ALL.