 The TEL/AML1 fusion associated with t(12;21)(p13;q22) is the most common gene rearrangement in childhood malignancy, occurring in approximately 25% of pediatric acute lymphoblastic leukemia.     ///    The TEL/AML1 fusion does not occur in children with AML and suggests that the TEL/AML1 rearrangement is restricted in pediatric hematologic malignancy to B lineage ALL..     ///    The TEL/AML1 rearrangement is cryptic at the cytogenetic level but confers a favorable prognosis.     ///    An RT-PCR assay was then used to test for the presence of the TEL/AML1 fusion.     ///    Lack of TEL/AML1 fusion in pediatric AML: further evidence for lineage specificity of TEL/AML1..     ///    Zero out of 29 pediatric AML patients had evidence for the TEL/AML1 fusion by RT-PCR.     ///    We have therefore determined the frequency of the TEL/AML1 fusion in pediatric myeloid leukemias by RT-PCR analysis. 