Detection of the Mbcr/abl translocation in chronic myeloid leukemia by fluorescence in situ hybridization: Comparison with conventional cytogenetics and implications for minimal residual disease detection

Abstract

The correlation between the detection of the Philadelphia chromosome by conventional cytogenetics and the identification of Mbcr/ abl translocation by fluorescence in situ hybridization (FISH) in both metaphase and interphase cells is prospectively analyzed in a group of 21 chronic myeloid leukemia (CML) patients. To gain insight into the sensitivity and specificity of the detection of the bcr/abl translocation by FISH, a group of 10 healthy volunteers was also studied. Our results show that for the detection of bcr/abl translocation in CML patients, FISH is more sensitive than conventional cytogenetics because it detects significantly higher proportions of cells carrying the translocation both in metaphase ( P < .0002) and interphase nuclei ( P < .003). Moreover, in the metaphases of the controls analyzed, no bcr/abl+ chromosome was detected that makes the colocalization of bcr and abl signals in the CML patients highly specific. Conversely, in control interphase nuclei, a small proportion of cells (ranging between 0% and 3%, mean value of 1.7% ± 0.9%) displaying colocalization of both signals is usually detected. This limits, at least for the moment, the routine use of FISH for the detection of minimal residual disease in CML patients at levels lower than 10 −1.