Expression of the ABL-BCR fusion gene in Philadelphia-positive acute lymphoblastic leukemia..     ///    " We have previously shown that the chimeric gene ABL-BCR, formed on the derivative chromosome 9q+ as a result of the t(9;22) translocation, is transcriptionally active in 65% of chronic myeloid leukemia patients. "    ///    "in two cases, ABL-BCR transcripts with the Ia-e2 junction type were also present. "    ///    All seven patients with P190 had ABL-BCR transcripts containing a junction between ABL exon Ib and BCR exon 2 (Ib-e2).     ///    "Of the two P210 ALL patients, one had a Ib-b4 ABL-BCR transcript and the other showed no detectable ABL-BCR expression. "    ///    "We have now used the same technique, reverse transcription/polymerase chain reaction amplification of ABL-BCR transcripts, to study nine patients with Philadelphia (Ph) chromosome-positive acute lymphoblastic leukemia (ALL). "    ///    "Although the BCR-ABL gene is probably fundamental in the pathogenesis of the Ph+ leukemias, differential expression of the ABL-BCR gene could contribute to the biologic heterogeneity of the disease.. "