The t(12;21) translocation resulting in TEL/AML1 gene fusion is present in approximately 25% of patients with precursor B-lineage pediatric acute lymphoblastic leukemia (ALL). Studies suggest an association with a good prognosis; however, relapse can occur. We studied the relation between t(12;21), determined by fluorescence in situ hybridization or polymerase chain reaction, and in vitro drug resistance, measured by the MTT assay, in childhood B-lineage ALL at diagnosis. A total of 180 ALL samples were tested, 51 (28%) of which were positive for t(12;21). The median LC(50) values did not differ significantly between TEL/AML1-positive and -negative samples for prednisolone, dexamethasone, daunorubicin, thiopurines, epipodophyllotoxins, and 4-HOO-ifosfamide. However, the TEL/AML1-positive patients were relatively more sensitive to L-asparaginase (ASP; 5.9-fold; P =.029) and slightly but significantly more resistant to vincristine (1.5-fold; P =.011) and cytarabine (1.5-fold; P =.014). After matching for unevenly distributed patient characteristics-that is, excluding patients younger than 12 months, patients with CD10-negative immature B-lineage ALL, patients with Philadelphia chromosome, and patients who were hyperdiploid (more than 50 chromosomes) from the TEL/AML1 negative group-the only remaining difference was a relative sensitivity for ASP in the TEL/AML1-positive samples (10.8-fold; P =. 012). In conclusion, the presence of TEL/AML1 gene fusion in childhood precursor B-lineage ALL does not seem to be associated with a high in vitro drug sensitivity, except for ASP, indicating that these patients could benefit from treatment schedules with significant use of this drug.
