title: 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.
abstract: BACKGROUND
  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). The signal constellation on metaphases with the tri-colour dual fusion system was defined. The knowledge of various signal patterns obtained from the different genetic rearrangements was further applied to the analysis of hybridization signals on interphase nuclei.
  
  
  METHODS
  BCR-ABL1 dual colour, dual fusion FISH (D-FISH) was performed on diagnostic samples of 22 CML patients. The tri-colour FISH system was performed on cases that showed aberrant signal patterns other than the classical 1 green (G) 1 orange (O) 2 fusions (F). Using the aqua band-pass filter, random signal overlap in interphase nuclei would be indicated by the presence of an aqua signal (ASS1), while genuine fusion was represented by the absence of the ASS1 signal.
  
  
  RESULTS
  Using the D-FISH system, the signal patterns could be categorized into 4 groups: group 1 (n = 17) showed the classical 1G1O2F; group 2 (n = 2) showed 2G1O1F indicating ABL1 deletion; group 3 (n = 1) showed 1G2O1F indicating BCR deletion; group 4 (n = 2) with 1G1O1F indicating reciprocal ABL1-BCR deletion. The tri-colour dual fusion system correlated with the D-FISH system for cases with der(9) 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).
  
  
  CONCLUSIONS
  Although the D-FISH probe was valuable in establishing the different patterns of aberrant signals and monitoring patients with the classic 2-fusion signals in CML, the tri-colour dual fusion probe should be used for patients with der(9) deletion to monitor response to treatment.
authors: Department of Pathology, Queen Elizabeth Hospital, Hong Kong SAR, PR China.
authors: Lisa Lp
authors: LL
authors: Siu
authors: Division of Molecular Pathology, Department of Pathology, Hong Kong Sanatorium & Hospital, Hong Kong SAR, PR China.
authors: Edmond Sk
authors: ES
authors: Ma
authors: Department of Pathology, Queen Elizabeth Hospital, Hong Kong SAR, PR China.
authors: Wai Shan
authors: WS
authors: Wong
authors: Department of Medicine, Queen Elizabeth Hospital, Hong Kong SAR, PR China.
authors: Man Hong
authors: MH
authors: Chan
authors: Department of Pathology, Queen Elizabeth Hospital, Hong Kong SAR, PR China.
authors: Kit Fai
authors: KF
authors: Wong