Detection Limit of Minimal Residual Disease in Leukemia Using Fluorescence in situ Hybridization

Purpose : The close relationship between the size of a tumor burden and the curability of acute leukemia is well established. Therefore, it is very important to detect residual leukemia accurately at low levels. Fluorescence in situ hybridization(FISH) techniques rely on chromosome-specific and gene specific DNA probes to identify numerical and structural chromosomal abnormalities. But the detection limit of FISH in residual leukemia is still uncertain. So we evaluated the detection limit of residual leukemic cells with the chromosomal abnomualities on FISH. Methods : Cells with monosomy, trisomy and bcr/abl fusion were admixed with normal diploid cells in different concentrations of 0%, 0.1%, 0.5%, 1%, 2.5%, 5%, 10%, 20% and 100%. Monosomy and trisomy cells were hybridized with chromosome 1 or 8 or X centromeric probes, and the cells with bcr/abl fusion were hybridized with bcr/abl probe and detected using FISH technique. The number of signals from 150 to 1000 cells were counted. Results : The detection limit was 1% in monosomy assay and 0.5% in trisomy and translocation assay. The proportion of cells showing each signal increased according to the increase of mixed cells. Conclusion : FISH for detection of minimal residual leukemia is a sensitive and specific method which could detect at least 1% leukemic cells in the samples. Especially, cells with trisomy or translocation could be more easily detected. It could be also used for quantitative monitoring of leukemic cells. (J Korean Pediatr Soc 2000;43:1364-1371)