BCR-ABL1 dual colour, dual fusion FISH (D-FISH) was performed on diagnostic samples of 22 CML patients.     ///    "Application of tri-colour, dual fusion fluorescence in situ hybridization (FISH) system for the characterization of BCR-ABL1 fusion in chronic myelogenous leukaemia (CML) and residual disease monitoring.. "    ///     We studied the application of the BCR-ABL1 + 9q34 tri-colour dual fusion fluorescence in situ hybridization (FISH) system in the characterization of fusion signal pattern and the monitoring of residual disease in chronic myelogenous leukaemia (CML).     ///    group 4 (n = 2) with 1G1O1F indicating reciprocal ABL1-BCR deletion.     ///    The added aqua-labelled ASS1 probe was useful in differentiating random signal overlap from genuine BCR-ABL1 fusion in the interphase cells (group 4). 