The value of interphase fluorescence in situ hybridization for the detection of translocation t(12;21) in childhood acute lymphoblastic leukemia

ETV6/CBFA2 fusion by means of FISH, using two cosmid probes mapped on ETV6 and on CBFA2 , respectively. The cut-off value (mean + three standard deviations) for positivity established on control patients was 9.3%. A comparison between FISH and molecular methods [reverse-transcriptase polymerase chain reaction/Southern blot (RT-PCR/SB)] was possible in 52 patients: 34 of 52 (65.4%) showed negative results with both approaches, and 13 of 52 (25%) were positive; 5 of 52 (9.6%) showed discrepancies: four patients who were positive using RT-PCR/SB were negative using FISH. Conversely, one patient negative when using RT-PCR/SB was positive with FISH. Further investigations on this patient, cytogenetically characterized by add(12p), showed an atypical breakpoint on ETV6 , located 5′ to the common breakpoint. Compared with RT-PCR and SB, dual-color interphase FISH with the cosmid probe set proved to be highly specific but showed limited sensitivity.