Incidence of TEL/AML1 fusion in children with relapsed acute lymphoblasticleukemia

The TEL/AML1 fusion associated with t(12;21)(p13;q22) is the most common ge ne rearrangement in childhood leukemia, occurring in approximately 25% of p ediatric acute lymphoblastic leukemia (ALL), and is associated with a favor able prognosis. For example, a cohort of pediatric patients with ALL retros pectively analyzed for the TEL/AML1 fusion treated on Dana-Farber Cancer In stitute (DFCI) ALL Consortium protocols between 1980 to 1991 demonstrated a 100% relapse-free survival in TEL/AML1-positive patients with a median of 8.3 years of follow-up, However, two recent studies analyzing pediatric pat ients with relapsed ALL have reported the same incidence of the TEL/AML1 re arrangement as in patients with newly diagnosed ALL, suggesting that TEL/AM L1 positivity is not a favorable prognostic indicator. To clarify this appa rent discrepancy, 48 pediatric patients treated on Dana-Farber Cancer Insti tute (DFCI) protocols with ALL at first or second relapse were tested for T EL/AML1 using reverse transcriptase-polymerase chain reaction (RT-PCR). The TEL/AML1 fusion was identified in only 1 of 32 analyzable relapsed ALL pat ients, in concordance with our previous reports of improved disease-free su rvival in TEL/AML1-positive patients. The low frequency of TEL/AML1-positiv e patients at relapse is significantly different than that reported in othe r studies. Although there are several potential explanations for the observ ed differences in TEL/AML1-positive patients at relapse, it is plausible th at relapse-free survival in TEL/AML1-positive patients may be changed with different therapeutic approaches. Taken together, these results support the need for prospective analysis of prognosis in TEL/AML1-positive patients. (C) 1998 by The American Society of Hematology.