Currently the quantitative detection of clonal-specific rearrangements of immunoreceptor genes (T-cell receptors and immunoglobulins) is considered to be the standard approach in minimal residual disease (MRD) monitoring in childhood acute lymphoblastic leukaemia. However, optimisation of two independent rearrangements with sensitivity of at least one malignant cell among 10 000 normal cells is not successful in all patients. TEL/AML1 fusion gene is the most common chromosomal aberration in childhood acute lymphoblastic leukaemia and is present in more than 20% of patients. Comparison of residual disease levels examined simultaneously by quantitative polymerase chain reaction on TEL/AML1 transcript and on immunoreceptor gene rearrangements in 41 samples showed very good overall correlation with only two exceptions (R2=0,847). Thus, quantitative detection of TEL/AML1 transcript can serve as an alternative target for MRD monitoring in patients with TEL/AML1-positive leukaemia and a lack of sensitive standard markers – immunoreceptor gene rearrangements. Among 52 patients with residual disease level tested at the end of induction therapy, the presence ofTEL/AML1- positive cells reliably separated patients with poor prognosis (relapse free survival = 50%, 7 relapses in 14 patients) from children with excellent outcome (relapse free survival = 92%, 3 relapses in 38 patients, p=0,0007). Detectable TEL/AML1-positive cells at the end of induction therapy thus predict relapse with a high probability even though the relapse occurs 57 months from the original diagnosis.

        Key words: childhood acute lymphoblastic leukemia, TEL/AML1, quantitative PCR, minimal residual disease