Detection of residual proliferating leukemic cells by fluorescence in situ hybridization in CML patients in complete remission after interferon treatment.
Interferon-alpha produces a complete hematologic and cytogenetic remission in approximately 20% of patients with chronic myelogenous leukemia (CML). In this study, we applied fluorescent in situ hybridization (FISH) methodology to examine the possibility that a low level of proliferating Philadelphia-chromosome-positive (Ph+) cells may be present in interferon-treated CML patients who have achieved complete cytogenetic remission (as defined by the absence of Ph chromosome in 20-25 metaphases analyzed). Ten such patients in remission for 6-35 months were studied by this technique, in which a chromosome-22-specific DNA painting probe was used to detect leukemic cells with the characteristic 9;22 chromosomal translocation. In six of the 10 patients (60%), 3-9% Ph+ metaphases were detected. No Ph+ cells were observed in nine control individuals. Thus, this study demonstrates that FISH technology is more sensitive than conventional cytogenetic analysis for the detection of minimal residual disease in CML.