Minimal residual disease studies are beneficial in the follow-up of TEL/AML1 patients with B-precursor acute lymphoblastic leukaemia

The t(12;21)(p13:q22) translocation has been identified as the most common chromosomal abnormality in childhood acute lymphoblastic leukaemia (ALL), I nitially several investigators reported an excellent prognosis in paediatri c leukaemias with this translocation, but other studies showed a 20% incide nce in relapsed ALL. We performed an extensive analysis of 90 ALL patients. In 17 (19%) cases a TEL/AML1 fusion was found. However this group was not representative as it included a high number of relapsed patients compared w ith the normal incidence in B-precursor ALL [54 in continuous complete remi ssion (CCR) and 36 relapsed patients] and only a slightly better prognosis for TEL/AML1-positive patients was found (not significant) (four relapses i n 17 TEL/AML1-positive patients vs. 32 relapses in 73 TEL/AML1-negative pat ients). Comparison of known prognostic factors (age, sex, ploidy white bloo d cell count and immunophenotype) between relapsed TEL/AML1-positive and TE L/AML1-positive patients in CCR did not reveal differences, except that the white blood cell count was significantly higher in the relapsed group (P = 0.001). Time between diagnosis and relapse was not different for the relap sed TEL/AML1-positive group vs, the relapsed TEL/AML1-negative group. In 11 TEL/AML1-positive patients, the minimal residual disease (MRD) level at th e end of induction therapy was quantified in a limiting dilution assay usin g IGH or TCRD junctional regions as polymerase chain reaction (PCR) targets . In all four relapsed patients, the level of MRD at the end of induction t herapy was high (range 0.24-1.2%), whereas in all seven CCR patients, the M RD level was extremely low (0.02 to <0.001%). In agreement with previous st udies in which MRD levels at the end of induction therapy were found to be the strongest risk factor independent of other risk factors, in the present study we show that the MRD level remains a risk factor independent of the presence of a TEL/AML1 fusion gene.