Cytogenetic And FISH Studies Of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a clonal hematological malignancy arising from hematopoietic stem cells. The clonal chromosomal abnormalities of AML are significantly valuable not only for diagnosis and classification, but also for its prognosis and treatment. At present, adult AML karyotype abnormality rate is about 54% -78%. There are still about 45% of cases with normal karyotype. AML with normal karyotype show a great heterogeneity in the response to treatment and in survive. About 10% -12% of AML with the complex karyotypic abnormalities could not be exactly elucidated only by conventional cytogenetic (CC) analysis. Recently, many scholars found some cryptic chromosomal abnormalities which were not detected by CC with the application of new molecular cytogenetic and molecular biologic techniques.【Objective】To analysis the cytogenetic characteristics of 317 cases of de novo AML in china, to detect the specific chromosome rearrangements using interphase-FISH and to evaluate the value of M-FISH as a new molecular genetic technology in clarifing the nature of the complex chromosomal abnormalities.【Methods】All cases were studied by R-band karyotypic analysis using direct method and/or short-term culture for chromosomes preparation. Interphase-FISH was performed in 108 cases of AML with M5, M4, M2, M3 subtypes including 103 cases with normal karyotype, 4 cases with chromosomal abnormalities other than specific chromosomal rearrangements and one without metaphase cells and 19 cases of AML with trisomy 22 using chromosome translocation probe such as AML1/ETO, PML/RARα, CBFβ/MYH11 and MLL. M-FISH, chromosome painting and interphase-FISH were performed in 12 cases of AML with complex karyotypic abnormalities.【Results】1 Of the 317 AML cases, CC revealed clonal karyotypic abnormalities in 175 cases, normal karyotype in 142 cases. Thus, the detection rate of abnormal karyotypes was 55%. Among structure abnormalities, specific chromosomal rearrangement was the most frequent, seen in 103 cases, accounting for 59% of AML cases with abnormal karyotypes. Of them, t(15;17) was the most common, seen in 55 cases with M3 subtype. Their median WBC count was lower than that of the AML cases with normal karyotype, the CD34 and HLA-DR expression in their leukemia cells were weak or negative. Their complete remission (CR) rate was the most high. The difference of CR rates between t(15;17) group and normal karyotype group was significant in statistics. The next was t (8;21), seen in 40 cases, of which 80% belonged to M2 subtype, accounting for 32.7% of M2-AML. Their median WBC count was lower than that of AML with normal karyotype. They often expressed CD19 antigen besides myeloid antigens. Their CR rate was 92% which was higher than that of AML with complex karyotypic abnormalities. Inv(16) was seen in 3 cases. Their CR rate was 100%. 11q23 rearrangement was seen in 5 cases, of which 4 had t(9;11) presenting M5 subtype, one had t(11;19) presenting M2 subtype. T(9;22) was seen in only two cases with M5 and M6 subtype, respectively. Complex karyotypic abnormalities were seen in 22 cases including 5 M5 and 5 M6 subtypes. Their CR rate (38%) was the lowest. Of them, 11 cases died with a median survival of 5 months. The survival rate of t(8;21), t(15;17) and normal karyotype groups were higher than that of complex karyotypic abnormalities group.Their differences were significant in statistics.2 Of 38 cases of M2-AML without t(8;21) on CC analysis, 4 cases showed positivity for AML1/ETO fusion transcript, including 2 cases with typical signal model and 2 with insertion .Of 9 cases of M3-AML without t(15;17) on CC analysis , 6 showed positivity for PML/RARαfusion transcript including 2 with typical signal model, 3 with insertion , one without PML/RARαrearrangement on PT-PCR and FISH assay using PML/RARαprobe , but showing RARαpartial deletion on FISH assay using the RARαdual color, break apart rearrangement probe. Of 23 cases with M4 or M4EO-AML without inv(16) on CC analysis, 3 showed positivity for CBFβ/MYH11 fusion transcript . Of 38 cases without 11q23 translocation on CC analysis, all cases were negative for MLL rearrangement. Of 19 cases with trisomy 22 on CC analysis, 13 (68.4%) showed positivity for CBFβ/MYH11 fusion transcript, including M4EO 7 cases, M5 3 cases, M2 2 cases and M1 one case. Of 14 cases with CBFβrearrangement and the follow-up data, 10 survived, only one died, however, all there cases without CBFβrearrangement died. 3 M-FISH elucidated the origin of mark chromosomes in 6 cases, clarified the nature of the derivative chromosomes in two cases, detected new derivative chromosomes in 8 cases in addition to confirmation of the abnormalities detected by CC analysis. The derivative chromosomes resulted from unbalanced translocations, most of which were missed as chromosome deletion, additional material of unknown origin, monosomy and marker chromosome. Chromosome painting confirmed the results of M-FISH in most cases.【Conclusion】1,The detection rate of abnormal karyotype was 55% in this series, of which specific chromosome translocations accounted for 59%, normal karyotype was seen in 45% AML cases.2,This study confirmed that chromosome karyotype have important prognostic significance: t(8;21) and t(15;17) AML had better prognosis, however, AML with complex karyotypic abnormalities had the worst prognosis in AML cases.3,Interphase-FISH could detect the specific chromosome rearrangements such as AML1/ETO, PML/RARαor CBFβ/MYH11 in some cases with normal karyotype, with chromosome abnormalities other than specific chromosomal translocations or without metaphase cells, however, it seen less useful for the detection of MLL rearrangement.4,Sole trisomy 22 had predictable effect for inv(16).5,M-FISH is helpful to elucidate the origin of marker chromosome and clarify the nature of unbalanced translocation for derivative chromosomes seen in complex karyotypic abnormalities.6,CC is a basic examination, FISH is an important complement to CC. The combination of both will provide more comprehensive genetic information.