Three out of the 14 patients positive for the TEL/AML1 gene fusion were originally reported to be culture failures and none of the remaining eleven samples had been found to have chromosome 12 abnormalities by conventional cytogenetic techniques.     ///    All fourteen patients positive for TEL/AML1 gene fusion were mosaic.     ///    one did have the TEL/AML1 gene fusion.     ///    " To investigate patients with acute lymphoblastic leukemia (ALL) for TEL/AML1 fusion, BCR/ABL fusion, MLL gene rearrangements, and numerical changes of chromosomes 4, 10, 17 and 21 by fluorescence in situ hybridization (FISH) and to determine the relationship and the significance of those findings. "    ///    "Interestingly, seven of these patients did not have TEL/AML1, BCR/ABL or the MLL gene rearrangement. "    ///    All pediatric patients with pre-T or T cell lineage and the six adults were negative for TEL/AML1 fusion.     ///    Four patients had a monosomy of chromosome 17 and three out of these patients with monosomy 17 also had a fusion signal of TEL/AML1.     ///    "14 out of the 45 pediatric patients (31%) were positive for TEL/AML1 fusion, among which three had an additional derivative 21 [t (12;21)], four had a deletion of 12p and two had an extra copy of chromosome 21. "    ///    All 14 patients with positive TEL/AML1 fusion had ALL pre-B cell or B-cell lineage according to standard immunotyping.     ///    "This study found a trend towards a division between patients who had structural changes such as t (12;21) or a ring chromosome 21 and those who had numerical changes of chromosome 21 as well as the patients with TEL/AML1 fusion and patients with the coexistence of numerical chromosomal changes of chromosomes 4, 10 and 17. "