OBJECTIVETo evaluate the clinical significance of the application of fluorescence in situ hybridization (FISH) in detecting chronic myeloid leukemia (CML).

METHODSChromosome preparation was made by using 24-hour culture. FISH technique using dual color dual fusion (DC-DF) BCR/ABL probe was performed in all 158 cases and R-banding was also employed for karyotyping in some patients.

RESULTSAmong the 158 cases, 98 cases were Ph positive, of which 69 cases (70.4%) were typical FISH pattern (1R1G2F), the other 29 cases (29.6%) showed 12 different types of atypical FISH pattern. The most frequent atypical patterns found were 1R1G1F in 7 cases (7.1%), 2R1G1F in 5 cases (5.1%), 1R1G2F and 1R1G3F in 4 cases (4.1%), 2R2G1F in 3 cases (3.1%). Karyotype analysis on 18 CML cases with atypical FISH patterns demonstrated that the atypical FISH patterns were due to variant translocation in 3 cases; the additional third signal was because of a supernumerary Ph chromosome. The karyotyping results did not conform to FISH results in four cases suggesting the conceivable mistakes in karyotyping. The 1R1G1F signal pattern seen in 3 cases with classical t(9;22) resulted from the deletion of derivative chromosome 9. The 1R1G2F signal pattern detected in 40% to 64% of interphase cells of 3 cases without Ph chromosome by conventional cytogenetic analysis suggested a submicroscopic translocation. Three cases treated with Glivec or bone marrow transplantation showed normal karyotypes with a small amount of BCR/ABL positive cells by FISH detection.

CONCLUSIONFISH technique is of great value for the diagnosis of CML and confirmation of variant translocation, occult Ph translocation, derivative chromosome 9 deletion, therapeutic effect of interferon and Glivec as well as detection of minimal residual disease after bone marrow transplantation.