Variant t(8;21) rearrangements in acute myeloblastic leukemia of childhood

[A Case of Acute Myeloid Leukemia with Masked t(8;21).]

We report a case that revealed the characteristics of acute myeloblastic leukemia with maturation (AML-M2) on the morphology of the bone marrow biopsy and 45,X,-Y in conventional cytogenetic study, but was confirmed to have a typical AML1/ETO translocation by molecular studies using reverse transcriptase polymerase chain reaction and fluorescence in situ hybridization. Insertion of ETO gene on chromosome 8 into chromosome 21 in this patient resulted in the development of the chimeric gene, AML1/ETO, on the long arm of chromosome 21. Our final report on the patient's karyotype: 45,X,-Y.ish ins(21;8)(q22;q22q22)(AML1 +,ETO +;ETO +,AML1-). In case typical morphologic features compatible with recurrent cytogenetic abnormalities are shown, molecular studies in addition to conventional cytogenetic study might be required to confirm the diagnosis.

RUNX1 translocations and fusion genes in malignant hemopathies

The RUNX1 gene, located in chromosome 21q22, is crucial for the establishment of definitive hematopoiesis and the generation of hematopoietic stem cells in the embryo. It contains a 'Runt homology domain' as well as transcription activation and inhibition domains. RUNX1 can act as activator or repressor of target gene expression depending upon the large number of transcription factors, coactivators and corepressors that interact with it. Translocations involving chromosomal band 21q22 are regularly identified in leukemia patients. Most of them are associated with a rearrangement of RUNX1. Indeed, at present, 55 partner chromosomal bands have been described but the partner gene has solely been identified in 21 translocations at the molecular level. All the translocations that retain Runt homology domains but remove the transcription activation domain have a leukemogenic effect by acting as dominant negative inhibitors of wild-type RUNX1 in transcription activation.

Molecular cytogenetic investigations in a novel complex variant of t(8;21)(q22;q22) with ins(15;21)(q15;q22.2q22.3) in a patient with AML-M2 subtype

Acute myeloid leukemia (AML) is a clinically and molecularly heterogeneous disease characterized by the aberrant proliferation of myeloid stem cells, reduced apoptosis and blockage in cellular differentiation. The present report describes the results of hematological, cytogenetic, and fluorescence in situ hybridization (FISH) analysis in a 25-year-old man diagnosed with AML-M2. Cytogenetic as well as FISH analysis revealed a complex translocation involving four chromosomes, with the karyotype 45,-Y,der(X)t(X;8)(p21;q22),der(8)t(8;21)(q22;q22),ins(15;21)(q15;q22.2q22.3),der(21)t(8;21)(q22;q22). The breakpoints at 8q22 and 21q22 suggested a rearrangement of the RUNX1T1 (alias ETO) and RUNX1 (previously AML1) genes, respectively. Using a dual-color FISH test with RUNX1T1 and RUNX1 probes, we demonstrated an RUNX1/RUNX1T1 fusion signal on the derivative chromosome 8, establishing this translocation as a novel complex variant of t(8;21)(q22;q22).

A variant t(8;10;21) in a patient with pathological features mimicking atypical chronic myeloid leukemia

We report the case of an 11-year-old girl who was initially diagnosed with a chronic myeloproliferative disorder, possibly chronic myelogenous leukemia (CML), based on laboratory and blood and marrow morphological findings. The patient's high leukocyte count did not respond to hydroxyurea, a standard initial therapy for CML. Chromosomal analysis revealed that the patient did not have t(9;22), but a complex t(8;10;21)(q22;q24;q22), a variant of t(8;21). The treatment regime was switched to an acute myeloid leukemia (AML) protocol; the patient responded well and is now in remission. This case demonstrates again that routine clinical cytogenetic analysis plays an important role in the clinical diagnosis, guidance of treatment, and prognostication in hematological disorders.

Breakpoints of variant 9;22 translocations in chronic myeloid leukemia locate preferentially in the CG-richest regions of the genome

From 5% to 10% of 9;22 translocations in chronic myeloid leukemia (CML) are reported to occur in variant form, that is, with the involvement of other regions of the genome in 3-way or more rearrangements. The literature indicates that the alternative breakpoints are not distributed randomly in the genome but show hotspots. We present data on 289 unpublished cases of CML with variant 9;22 translocations having a total of 342 variant breakpoints, the largest independent series to date. We found that the distribution of breaks was in loose agreement with the literature but that some new hotspots were identified; furthermore, some published hotspots were not fully supported by our data. Moreover, when our 342 variant breakpoints were plotted against profiles of CG heterogeneity in the genome, a significant positive correlation between breakpoint locations and CG composition was observed. In an ancillary study, we compared the frequency of variant t(9;22) with that of variants of t(15;17) associated with acute promyelocytic leukemia (AML M3). We found that the frequency of the former, 9.3%, was significantly higher than that of the latter, 2.6%.

Complex translocation (8;12;21): a new variant of t(8;21) in acute myeloid leukemia

Variants of the t(8;21)(q22;q22) involving chromosomes 8, 21, and other chromosomes account for approximately 3% of all t(8;21)(q22;q22) in acute myeloid leukemia (AML) patients. In this paper, we report a case of AML-M2 with a t(8;12;21)(q22;p12 approximately p13;q22) associated with chromosomal abnormalities, including loss of the Y chromosome and trisomy 8q22 approximately qter. Using a dual-color fluorescence in situ hybridization (FISH) analysis with ETO and AML1 probes, we demonstrated an ETO/AML1 fusion signal on the derivative chromosome 8. Using whole painting probes for chromosomes 8 and 12, we demonstrated a three-way translocation, t(8;12;21)(q22;p12 approximately p13;q22). Reverse transcription polymerase chain reaction (RT-PCR) analysis showed the presence of AML1/ETO fusion transcript. The present case highlights the importance of the combination of approaches, i.e., standard karyotyping, FISH, and RT-PCR, for the detection of variants of t(8;21)(q22;q22), shedding light on region 8q22 approximately qter which could harbor potential genes responsible for leukemogenesis.

Monitoring of minimal residual disease (MRD) by real-time quantitative reverse transcription PCR (RQ-RT-PCR) in childhood acute myeloid leukemia with AML1/ETO rearrangement

The fusion transcript AML1/ETO corresponding to translocation t(8;21)(q22;q22) can be found in approximately 7-12% of childhood de novo AML. Despite the favorable prognosis, some of these patients relapse. Most of MRD studies so far were performed on adults treated not uniformly. Therefore, we analyzed the follow-up of 15 AML1/ETO-positive children using real-time quantitative reverse transcription PCR (RQ-RT-PCR), all enrolled in the multicenter therapy trial AML-BFM 98. AML1/ETO copy numbers were normalized to the control gene ABL and the results were expressed in copy numbers AML1/ETO per 10 000 copies ABL. At diagnosis, a median of 10 789 copies AML1/ETO was found. A linear decrease to about 10 copies (2-4 log) could be seen in most of the children by the start of consolidation. In the majority of cases they remained positive at this low level during the ongoing therapy. Four children relapsed and two of them had a decrease of less than 2 log before starting consolidation. Three of the relapsed children showed, prior to relapse, an increase of the AML1/ETO fusion transcript at 6, 9, and 11 weeks, respectively. These results suggest that monitoring of minimal residual disease using RQ-RT-PCR could be helpful in detecting patients with a higher risk of relapse.

Cryptic chromosomal aberrations leading to an AML1/ETO rearrangement are frequently caused by small insertions

The translocation t(8;21)(q22;q22), which results in the fusion of the AML1 (RUNX1) and ETO (CBFA2T1) genes, is a recurrent aberration in acute myeloid leukemia (AML), preferentially correlated with FAB M2, and has the highest incidence in childhood AML. Because of the favorable prognosis, the evidence of the t(8;21) or the AML1/ETO fusion gene is mandatory in most of the therapy trials, allowing the stratification of the patients to the correct risk group in terms of treatment. Here we present six out of 59 children with AML who were positive for AML1/ETO by RT-PCR, but showed no evidence of the classical t(8;21)(q22;q22) by conventional cytogenetics. Because of the discrepancies between molecular and cytogenetic analyses, these six patients were further investigated by fluorescence in situ hybridization analysis. Small hidden interstitial insertions resulting in an AML1/ETO rearrangement were detected in five (8.5%) of the 59 patients, whereas the sixth patient showed a cryptic three-way translocation. The insertions could be characterized as ins(21;8) in three patients and ins(8;21) in the remaining two. Additionally, three of the patients showed secondary chromosome aberrations leading to a higher complexity of the karyotype. In conclusion, the combination of more than one standard technique in the analysis of AML1/ETO is useful to reveal the overall frequency of cryptic chromosome rearrangements and permits a better understanding of the mechanisms involved in the generation of this fusion gene.

Genetic profile of acute myeloid leukemia

Understanding genomic events and the cascade of their effects in cell function is crucial for identifying distinct subsets of acute myeloid leukemia and developing new therapeutic strategies. Conventional cytogenetics, fluorescence in situ hybridization investigations and molecular studies have provided much information over the past few years. This review will focus on major genomic mechanisms in acute myeloid luekemia and on the genes implicated in the pathogenesis of specific subtypes.

t(8;21;8)(p23;q22;q22): a new variant form of t(8;21) translocation in acute myeloblastic leukemia with maturation

The complex variants of t(8;21) involving chromosomes 8 and 21 as well as a variable chromosome account for 1.1-5% of acute myeloid leukemia (AML) patients. This paper reports a case of AML-M2 with t(8;21;8) translocation for the first time. The patient was a female, aged 47 years. Her myelogram was compatible with AML-M2. Chromosome study using R-banding technique revealed a karyotype 46, XX, t(8;8)(p23;q22). Dual-color FISH assay with two probes P1 164(green signal) and YAC 225B8 (red signal) both of which closely located on the 8q showed that one yellow signal consisting of a green signal and a red signal and one red signal appeared on the long and the short arm of the same der(8) chromosome, respectively, further confirming this translocation occurred between both homologous chromosomes 8. RT-PCR analysis detected the AML1/ETO fusion transcript in our patient, thus indicating that this chromosomal aberration was, in fact, a complex three-way rearrangement t(8;21;8)(p23;q22;q22). In conclusion, combining conventional karyotype, FISH or RT-PCR analyses is a rational strategy for identification of the complex variants of t(8;21) translocation.

Two cases of AML (M2) with a t(8;19)(q22;q13): a new cytogenetic variant

"Simple" variants of the t(8;21) translocation involving chromosome 8 and a chromosome other than number 21 are rare. To our knowledge, only t(3;8)(q29;q22), t(8;11)(q22;q13), t(8;16)(q22;q24), t(8;20)(q22;p13), and t(8;22) have been reported in the literature. This paper describes for the first time two patients with acute myelogenous leukemia with a consistent t(8;19)(q22;q13) translocation. Their myelograms were compatible with the FAB-M2 subtype. The blasts from case 2 expressed CD34, CD33, CD13, and CD19. Karyotype analyses were performed on bone marrow cells using R- and G-banding at presentation. A t(8;19)(q22;q13) translocation was found in 28/30 metaphases for case 1 and in 23/25 metaphases for case 2. The latter case also had a deletion of chromosome 9, del(9)(q12q22) as an additional abnormality. Reverse transcriptase-polymerase chain reaction study revealed no AML1/ETO fusion transcript in case 2. Dual-color fluorescence in situ hybridization (FISH) assay using two probes (BAC92 and YAC412A4) convincingly demonstrated that the chromosomal material from 8q was translocated onto 19q rather than 19p in case 2. Thus, we consider t(8;19)(q22;q13) a true "simple" variant of t(8;21), and assume that a fusion gene resulting from the t(8;19) may contain the ETO gene located at 8q22 and an unknown partner gene from 19q13, which probably is a new transcription factor, whose molecular entity warrants further study.

Chromosomal rearrangements in childhood acute myeloid leukemia and myelodysplastic syndromes

Recurrent chromosomal abnormalities present in the malignant cells of children with acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) often correlate closely with specific clinical and biologic characteristics of the disease. Certain unique cytogenetic rearrangements are associated with distinct morphologic leukemic subtypes. These rearrangements should be detectable in most children with AML and MDS with the use of complementary molecular techniques such as fluorescence in situ hybridization (FISH), Southern blotting, and polymerase chain reaction. Apart from the diagnostic assessment, cytogenetic findings sometimes predict clinical outcome and thus also serve as prognostic parameters, which may affect the therapeutic decision. Alternative classifications of AML that take into account the genetic information are being proposed. Cytogenetic and molecular analyses may allow clinicians to more appropriately direct types of treatment. Abnormal fusion transcripts and chimeric proteins derived from karyotypic abnormalities now are being also targeted by novel therapeutic approaches.

Simple variant t(8;21) acute myeloid leukemias harbor insertions of the AML1 or ETO genes

We report on the molecular characterization of two acute myeloid leukemias (AML), one AML-M1 (patient 1) and one AML-M2 (patient 2) with t(8;21)(p21;q22) and t(8;20)(q22;p13), respectively, at diagnosis. The locations of the breakpoints, 21q22 in patient 1 and 8q22 in patient 2, prompted us to search for a cryptic t(8;21)(q22;q22) and involvement of the AML1 and ETO genes. Dual-color fluorescence in situ hybridization (FISH) using whole chromosome painting probes for chromosomes 8, 20, and 21 confirmed the conventional cytogenetic karyotypes. However, dual-color FISH using appropriate ETO and AML1 probes disclosed an insertion of AML1 into 8q22 on the derivative chromosome 8 in patient 1 and of ETO into 21q22 on one chromosome 21 in patient 2, leading to AML1-ETO fusion signals. Both cases expressed an AML1-ETO transcript, shown by reverse transcriptase polymerase chain reaction and cDNA sequencing. Creation of functional AML1-ETO fusion genes in these two simple variant t(8;21) probably occurred through complex mechanisms, combining translocation and insertion of chromosomal segments.

Granulocytic sarcoma in children with acute myeloblastic leukemia and t(8;21)

BACKGROUND

Granulocytic sarcomas (GS) have been associated with t(8;21). The prognosis of patients with GS is generally regarded as being less favorable than of patients with acute myeloblastic leukemia (AML). GS occurs relatively commonly in Africa and has been reported to affect 10-25% of black children presenting with AML. We sought to establish the incidence of GS in our pediatric population, to determine whether an association with t(8;21) existed, and to report on the outcome of these cases in a single series.

PROCEDURE

The records of consecutive pediatric patients treated for de novo AML in Johannesburg between January 1985-December 1995 were reviewed. Fifteen cases of GS among a total of 88 cases of AML presented to the Paediatric Haematology/Oncology Clinics of the Johannesburg and Baragwanath Hospitals. Fourteen (93%) of these patients were black male children.

RESULTS

All 9 cases of orbital GS (60%) and almost all cases with concurrent AML M2 had t(8;21). This translocation was present in only 4 n(8.5%) of the remaining 47 AML cases without GS for which cytogenetic data were available. One case presented with a complex chromosomal translocation not previously associated with GS. The median disease-free survival of the GS patients, using conventional chemotherapy treatment protocols, was significantly better than for the patients with AML and no GS (P = 0.0004).

CONCLUSIONS

Our data support a strong association between orbital GS, t(8;21), and AML M2 in the pediatric population. This entity occurred virtually exclusively in black male children at presentation. One third of these children who presented with AML had a GS. The favorable prognosis noted in our GS patients on standard induction and intensification therapy without local irradiation conflicts with some previous reports but is consistent with the favorable outcome documented in AML with t(8;21).

Cytogenetic and fluorescence in situ hybridization analyses of hematologic malignancies in Korea

Cytogenetic analysis was performed in 86 cases of hematologic malignancy, using conventional cytogenetic analysis and fluorescence in situ hybridization (FISH) analysis at two university hospitals in Korea between 1993 and 1995. In addition to well-known anomalies, some unusual abnormalities were found, such as t(17;22), trisomy 9 combined with t(14;17), (2;7) and Philadelphia chromosome in CML; t(1;12), t(11;22), t(9;17), and t(12;21) in AML; trisomy 11 in MDS; t(2;9) and complex t(8;8;13;14) in ALL. The results of FISH analysis in interphase nuclei using a translocation probe for CML and APL showed more than 85% positive cells in CML, and 75% positive cells in APL.

Molecular cytogenetics of childhood acute myelogenous leukaemias

Chromosome abnormalities of childhood acute myeloblastic leukaemia, observed at least in 70-80% of cases, are presently recognized as important parameters for diagnostic, prognostic and follow-up purposes. These abnormalities are numerical, structural or both numerical and structural. They are also classified in "primary" abnormalities, usually more or less related with one subtype of leukaemia, and "secondary" abnormalities thought to appear in a second time. Chromosome abnormalities of childhood acute myeloblastic leukaemia (AML) are not basically qualitatively different from those of adult AML. The main difference lies in the incidence of the various types of abnormalities, and these differences appear to be more marked for age extremes such as infants and elderly patients. In total, 3 common abnormalities are more frequently observed in childhood than in adult AML; t(8;21) in AML-M2, monosomy 7 in AML-M4, der(11q) in AML-M5. In addition, molecular rearrangements associated with chromosomal abnormalities are dependent on the type of rearrangement and not on age. As in adult AML, the prognostic value of chromosome abnormalities has been diversely evaluated; some anomalies seem to be related to a shorter survival than others independent of the various therapeutic protocols used. In the present work, chromosome abnormalities of childhood AML have been reviewed according to cytologic subtypes as well as to some clinical settings. Special attention has been paid to abnormalities frequently or exclusively encountered in children.

Identification of chromosome changes in acute myeloid leukemia (AML-M2) by molecular cytogenetics

Karyotyping with fluorescence in situ hybridization (FISH) is reported in two rare cases of AML-M2 FAB. In the first case FISH analysis confirmed the presence of a t(7;11)(p15:p15) translocation in a complex karyotype that also showed an unbalanced translocation involving the other chromosome 7, a rare rearrangement between chromosomes 9 and 20, and four or five copies of a small marker derived from chromosome 9. In the second case whole chromosome painting with probes for chromosomes 8, 14, and 21 revealed the presence of a masked t(8;21) translocation in which one chromosome 14 was involved in a newly discovered rearrangement, i.e., t(8;14;21)(q22-q24;q11;q22). Moreover , double color FISH using ETO-CDR P1 probe and a cosmid for the 5' part of AML-1 on chromosome 21 showed a two color signal on the 8q-, suggesting a recombination between ETO and AML 1. Molecular cytogenetics overcomes limitation of chromosome banding in the interpretation of complex rearrangements.

Cytogenetic survey of 53 Moroccan patients with acute myeloblastic leukemia

We present a cytogenetic survey of chromosome aberrations for 53 Moroccan patients with acute myeloblastic leukemia (AML). Our 53 patients were 2 to 70 years old with 31 men and 22 women. The cytogenetic study was performed with the following three methods: first, relative proportion of normal (N) or abnormal (A) metaphases; second, presence of specific or random abnormalities; and third, karyotype complexity. Among 36 patients (67%) with a chromosomal abnormality, 18 (34%) showed a specific aberration. We have found t(9;22) in three patients (5%), chromosome 5 or 7 abnormality in six (11%), del(11)(q23) in three (6%), +21 in four (8%), and +8 in two (4%). Specific translocations associated with FAB type were found: t(8;21) with AML2 in 12 patients (23%) and t(9;11) with AML5 in one (2%). Rare abnormalities were also found: one patient with t(7;21) associated with AML2 and another patient with r(1) ring associated with AML1. We concluded that our study in a Moroccan population confirmed the relation between some specific abnormalities and the FAB classification. We have found a higher incidence for t(8;21) than usually described. Finally, we have identified chromosomal abnormalities t(7;21)(q22;p11) and r(1), rarely described before.