Disappearance of AML1-MTG8(ETO) fusion transcript in acute myeloid leukaemia patients with t(8;21) in long-term remission

Clinical Application of Biomarkers for Hematologic Malignancies

Over the last decade, significant advancements have been made in the molecular mechanisms, diagnostic methods, prognostication, and treatment options in hematologic malignancies. As the treatment landscape continues to expand, personalized treatment is much more important.

With the development of new technologies, more sensitive evaluation of residual disease using flow cytometry and next generation sequencing is possible nowadays. Although some conventional biomarkers preserve their significance, novel potential biomarkers accurately detect the mutational landscape of different cancers, and also, serve as prognostic and predictive biomarkers, which can be used in evaluating therapy responses and relapses. It is likely that we will be able to offer a more targeted and risk-adapted therapeutic approach to patients with hematologic malignancies guided by these potential biomarkers. This chapter summarizes the biomarkers used (or proposed to be used) in the diagnosis and/or monitoring of hematologic neoplasms.;

A Focus on Intermediate-Risk Acute Myeloid Leukemia: Sub-Classification Updates and Therapeutic Challenges

Acute myeloid leukemia (AML) represents a heterogeneous group of hematopoietic neoplasms deriving from the abnormal proliferation of myeloid progenitors in the bone marrow. Patients with AML may have highly variable outcomes, which are generally dictated by individual clinical and genomic characteristics. As such, the European LeukemiaNet 2017 and 2022 guidelines categorize newly diagnosed AML into favorable-, intermediate-, and adverse-risk groups, based on their molecular and cytogenetic profiles. Nevertheless, the intermediate-risk category remains poorly defined, as many patients fall into this group as a result of their exclusion from the other two. Moreover, further genomic data with potential prognostic and therapeutic influences continue to emerge, though they are yet to be integrated into the diagnostic and prognostic models of AML. This review highlights the latest therapeutic advances and challenges that warrant refining the prognostic classification of intermediate-risk AML.

Comparison of spatial chromosomal organization between bone marrow and peripheral blood in acute myeloid leukemia

Acute myeloid leukemia associated with t(8;21)(q22;q22)/runt related transcription factor (RUNX)1-RUNX1 translocation partner 1 has been reported to exhibit a favorable outcome. The quantitative polymerase chain reaction is a reliable method for assessing minimal residual disease persistence, and peripheral blood (PB) samples are as informative as bone marrow (BM) samples during follow-up monitoring. However, few studies have compared the spatial organization of leukemia-specific chromosomes between BM and PB. In the present study, paired BM and PB samples were extracted from 6 patients with acute myeloid leukaemia-M2 and compared using three-dimensional fluorescence in situ hybridization. Cells were classified into three types: Normal, proximal and malignant. Comparisons of proportions (% of all cells) of different cell types revealed no significant difference between BM and PB samples. The relative radial positions (RRPs; d/R) of chromosomes 8 and 21 were consistent for 2/3 of BM and PB samples. The RRPs of chromosomes in proximal pairs were more interior in nuclei compared with chromosomes in normal pairs for BM and PB samples. The consistency of the spatial organization of chromosomes between BM and PB suggests that PB may be an alternative to BM for research and clinical diagnosis.

Clinical Relevance of RUNX1 and CBFB Alterations in Acute Myeloid Leukemia and Other Hematological Disorders

The translocation t(8;21), leading to a fusion between the RUNX1 gene and the RUNX1T1 locus, was the first chromosomal translocation identified in cancer. Since the first description of this balanced rearrangement in a patient with acute myeloid leukemia (AML) in 1973, RUNX1 translocations and point mutations have been found in various myeloid and lymphoid neoplasms. In this chapter, we summarize the currently available data on the clinical relevance of core binding factor gene alterations in hematological disorders. In the first section, we discuss the prognostic implications of the core binding factor translocations RUNX1-RUNX1T1 and CBFB-MYH11 in AML patients. We provide an overview of the cooperating genetic events in patients with CBF-rearranged AML and their clinical implications, and review current treatment approaches for CBF AML and the utility of minimal residual disease monitoring. In the next sections, we summarize the available data on rare RUNX1 rearrangements in various hematologic neoplasms and the role of RUNX1 translocations in therapy-related myeloid neoplasia. The final three sections of the chapter cover the spectrum and clinical significance of RUNX1 point mutations in AML and myelodysplastic syndromes, in familial platelet disorder with associated myeloid malignancy, and in acute lymphoblastic leukemia.

Acute myeloid leukemia--major progress over four decades and glimpses into the future

In this Review, the progress in research and therapy of acute myeloid leukemia is detailed.

Monitoring the AML1/ETO fusion transcript to predict outcome in childhood acute myeloid leukemia

BACKGROUND

To determine the prognostic significance of the detection of the minimal residual disease (MRD) in children with AML1/ETO AML, we compared the results of reverse-transcription polymerase chain reaction (RT-PCR) and quantitative reverse-transcription polymerase chain reaction (RQ-PCR).

PROCEDURE

Between January 2006 and February 2013, 70 patients (≤16 years of age) with AML1/ETO AML were included in our study. Bone marrow samples were evaluated using by both RT-PCR and RQ-PCR assays. AML1/ETO transcripts were normalized to 10(5) ABL copies.

RESULTS

When treated with fewer than four courses of therapy, no association was found between positive RT-PCR results and relapse. After four courses of therapy, a positive RT-PCR result was correlated with a probability of relapse. After induction chemotherapy, a >1.8 log reduction in AML1/ETO transcripts in BM determined by RQ-PCR may represent a subgroup of patients at low risk for relapse. MRD levels after consolidation (Courses 2 and 3) were also informative.

CONCLUSION

Both RT-PCR and RQ-PCR can be used to detect MRD in childhood AML1/ETO AML. RQ-PCR can identify patients who are at high risk of relapse earlier than can RT-PCR.

Minimal residual disease testing in acute leukemia

SUMMARY Predictive/prognostic factors in acute leukemia continue to be sought, in order to refine treatment strategies. Minimal residual disease (MRD) testing has been shown to be a statistically significant factor by multivariate analysis in both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia. Its utility in guiding therapy has been more extensively studied in pediatric ALL, with some protocols having instituted MRD testing into therapeutic algorithms. The clinical impact of MRD testing in ALL and acute myeloid leukemia will be presented, including both molecular and flow cytometric methodologies, with a more focused discussion of the strategy, methodology and interpretation of MRD testing by multiparametric flow cytometry.

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 Disease Eradication is a Prerequisite for Long-term Remission in Patients with t(8;21) Positive Acute Myeloid Leukemia: a Single Center Study

Association of long-term clinical remission and molecular disease-eradication is well established in acute myeloid leukemia (AML) patients with t(15;17) and inv(16). In patients with t(8;21) positive AML no consensus exists over the disappearance of the AML1/ETO fusion transcript during the course of disease and most studies reported reverse transcriptase polymerase chain reaction (RT-PCR) positivity as a common finding after consolidation chemotherapy, autologous and allogeneic stem cell transplantation (alloSCT). In our single center study, we performed RT-PCR monitoring in 14 patients with t(8;21) in CR1 (n = 13) and/or CR2 (n = 4). The median number of bone marrow (BM) and/or peripheral blood (PB) samples per patient was 18 (range, 2-43). In 5 out of 6 cases relapse occurred after persistence of minimal residual disease (MRD) in CR for 4-14 months. The sixth patient relapsed despite molecular remission (MR) in BM and PB for 3 months, molecular relapse preceded hematological relapse for 7 months. Eleven patients with a median follow-up of 7.8 (range, 1.5-15.4) years are in persistent CR and MR after consolidation chemotherapy (n = 7). mainly with repetitive cycles of high-dose Ara-C, autologous (n = 1) or myeloablative allogeneic (n = 3) stem cell transplantation. Molecular remission was attained immediately after alloSCT, but after 6-26 months in CR in patients with consolidation chemotherapy. In 7 patients, MRD was only studied in long-term remission. In conclusion, long-term CR was associated with persistent molecular disease-eradication. In our patients, molecular remission was a prerequisite but not a guarantee for long-term disease-free survival. Hematological relapse never occurred without prior molecular relapse. Due to the slow kinetics of AML1/ETO after consolidation chemotherapy the value of qualitative RT-PCR to predict early relapse is limited. In this situation quantitative RT-PCR might help to define individual relapse risk and to improve as well as facilitate clinical decision-making.

Quantitation of Minimal Residual Disease in Acute Myeloid Leukemia by Tryptase Monitoring Identifies a Group of Patients with a High Risk of Relapse

PURPOSE

Recent data suggest that tryptase is produced by blast cells in a group of patients with acute myeloid leukemia (AML). In these patients, serum tryptase levels are elevated at diagnosis and decrease to normal (<15 ng/mL) or near normal values in those achieving complete hematologic remission (CR) after chemotherapy.

PATIENTS

In this study, we examined the value of tryptase as a marker of minimal residual AML. In 61 patients with de novo AML exhibiting elevated serum tryptase (>15 ng/mL) at diagnosis, tryptase levels were measured serially during and after chemotherapy by a fluoroenzyme immunoassay.

RESULTS

Of the 61 patients, 42 (68.9%) entered hematologic CR in response to induction chemotherapy. Twenty-nine of these 42 patients also entered biochemical remission (BR) defined by a decrease of tryptase levels to normal (<15 ng/mL). The remaining 13 patients exhibited elevated enzyme levels despite of hematologic CR. As assessed by multivariate analysis, the elevated tryptase in CR was found to be an independent prognostic variable concerning disease-free survival. Thus, AML relapses occurred in 15 of 29 patients with CR + BR (52%) and in 12 of 13 patients with CR without BR (92%), resulting in a significantly reduced probability of continuous CR for patients with CR without BR (P < 0.05). In all patients with continuous hematologic CR, tryptase levels remained constantly normal, whereas a recurrent elevation of tryptase in CR was invariably followed by a hematologic relapse.

CONCLUSION

A persistently elevated tryptase level in AML in CR is indicative of minimal residual AML and associated with a high risk of relapse.

Prognostic value of real-time quantitative PCR (RQ-PCR) in AML with t(8;21)

Despite the favorable prognosis of patients with acute myeloid leukemia (AML) with t(8;21)(q22;q22) translocation, relapses still occur in about 30% of the cases but no initial factors can strongly predict the risk of relapse. Several recent studies suggest that monitoring minimal residual disease (MRD) may identify patients at risk of relapse. We prospectively monitored AML1-ETO rearrangement by real-time quantitative PCR (RQ-PCR) in 21 patients uniformly treated in our center. Blood (PB) and bone marrow (BM) samples were collected during and after therapy. At diagnosis, levels of AML1-ETO transcript showed large variations and there was a trend for a higher relapse rate in patients with high pretreatment expression levels (P=0.065). After induction therapy, absolute transcript levels (below 10(-3), compared to Kasumi cell line), or a greater than 3 log decrease by comparison to diagnosis levels, were significant predictors of the absence of relapse (P=0.02 and P=0.02, respectively). MRD levels after consolidation therapy were also significant indicators of relapse (P=10(-5)). Comparison of BM and PB samples showed similar sensitivity for detecting AML1-ETO transcript. In conclusion, RQ-PCR appears to be an early predictive factor of the relapse risk in AML with t(8;21). PB samples can be used adequately to evaluate the level of MRD by this technique.

Recurrence of acute myelogenous leukemia with the same AML1/ETO breakpoint as at diagnosis after complete remission lasting 15 years: analysis of stored bone marrow smears

The AML1/ETO fusion gene is expressed in virtually all patients with t(8;21)(q22;q22) acute myelogenous leukemia (AML). Long-term complete remission (CR) of AML with t(8;21) has been observed despite the presence of residual AML1/ ETO fusion transcripts, although detection may depend on the sensitivity of the methods used. We examined a patient with recurrent AML who showed the t(8;21)(q22;q22) chromosomal abnormality following a CR of 15 years. The blast cells at the time of recurrence expressed the AML1/ETO fusion transcript, and the breakpoint of the AML1 gene was located on intron 5. Southern blot analysis of the DNA extracted from bone marrow slides that had been made and stored for 15 years revealed the same rearrangement pattern of the AML1 gene. Furthermore, the junction sequences between the AML1 and the ETO genes, analyzed by long-distance inverse polymerase chain reaction, proved to be completely identical. These findings can be interpreted in two ways: (1) The initial leukemia clone persisted and finally relapsed after 15 years in the dormant state. (2) AML developed in different subclones having the same AML1/ETO junctional sequences but with additional genetic changes (second hit).

Core binding factor (CBF) acute myeloid leukemia: is molecular monitoring by RT-PCR useful clinically?

Clonal chromosomal abnormalities are the most important prognostic indicators in acute myeloid leukemia (AML). Two of the most prevalent cytogenetic subtypes of adult primary AML, t(8;21)(q22;q22) and inv(16)(p13q22)/t(16;16)(p13;q22), are characterized by disruption of the AML1(CBFA2, RUNX1) and CBFbeta genes, respectively, which encode subunits of core binding factor (CBF), a regulator of normal hematopoiesis. At the molecular level, t(8;21) and inv(16)/t(16;16) result in the creation of novel fusion genes, AML1/ETO and CBFbeta/MYH11, respectively, which encode fusion transcripts readily detectable by the reverse transcription-polymerase chain reaction (RT-PCR). Although the detection of t(8;21) or inv(16)/t(16;16) in adult patients with primary AML represents a favorable independent prognostic indicator for achievement of cure following intensive chemotherapy or stem cell transplantation, a substantial number of these patients (i.e. 40-50%) relapse and eventually die of their disease. Therefore, timely identification and therapeutic stratification of those patients deemed at high risk for disease relapse could ultimately result in a further improvement of clinical outcome within these cytogenetic subgroups of AML. As relapse is likely to occur as the result of failure of treatment to completely eradicate leukemic blasts, the detection of the AML1/ETO and CBFbeta/MYH11 fusion transcripts using sensitive RT-PCR assays has been utilized as a surrogate marker for resistant disease and, in turn, to predict disease recurrence during remission. The purpose of this paper is to review the applicability of this strategy to the clinical management of t(8;21) and inv(16)/t(16;16) primary AML, here collectively referred to as CBF AML.

Monitoring AML1-ETO and CBFbeta-MYH11 transcripts in acute myeloid leukemia

The core-binding factor (CBF) leukemias comprise acute myeloid leukemia (AML) with t(8;21) and inv(16)/t(16;16), characterized by the presence of the AML1-ETO and CBFbeta-MYH11 fusion genes, respectively. These leukemia-associated genes can now be sensitively and reliably quantified by real-time reverse transcription polymerase chain reaction (RT-PCR) techniques and thus can serve as molecular targets for monitoring residual leukemia. Studies to date suggest that quantitative monitoring of minimal residual disease (MRD) in CBF-positive AML is useful in distinguishing patients at high risk of relapse from those in durable remission. Preliminary results of MRD monitoring by real-time RT-PCR in this subset of AML patients are promising and provide the basis for further evaluation by quantitative analysis in large prospective clinical trials.

Detection of minimal residual disease in hematologic malignancies by real-time quantitative PCR: principles, approaches, and laboratory aspects

Detection of minimal residual disease (MRD) has prognostic value in many hematologic malignancies, including acute lymphoblastic leukemia, acute myeloid leukemia, chronic myeloid leukemia, non-Hodgkin's lymphoma, and multiple myeloma. Quantitative MRD data can be obtained with real-time quantitative PCR (RQ-PCR) analysis of immunoglobulin and T-cell receptor gene rearrangements, breakpoint fusion regions of chromosome aberrations, fusion-gene transcripts, aberrant genes, or aberrantly expressed genes, their application being dependent on the type of disease. RQ-PCR analysis can be performed with SYBR Green I, hydrolysis (TaqMan) probes, or hybridization (LightCycler) probes, as detection system in several RQ-PCR instruments. Dependent on the type of MRD-PCR target, different types of oligonucleotides can be used for specific detection, such as an allele-specific oligonucleotide (ASO) probe, an ASO forward primer, an ASO reverse primer, or germline probe and primers. To assess the quantity and quality of the RNA/DNA, one or more control genes must be included. Finally, the interpretation of RQ-PCR MRD data needs standardized criteria and reporting of MRD data needs international uniformity. Several European networks have now been established and common guidelines for data analysis and for reporting of MRD data are being developed. These networks also include standardization of technology as well as regular quality control rounds, both being essential for the introduction of RQ-PCR-based MRD detection in multicenter clinical treatment protocols.

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.

Minimal residual disease in acute myeloid leukaemia

Relapse remains the main cause of treatment failure in acute myeloid leukaemia (AML). Studies to date suggest that monitoring of minimal residual disease (MRD) in AML is useful in identifying patients at high risk of relapse from those in durable remission. This chapter describes the methodological advances in the detection of MRD and, in particular, focuses on the development of highly sensitive RT-PCR techniques, including real-time, for quantifying MRD. Preliminary results on the clinical utility of MRD monitoring in AML with t(8;21) and inv(16) are promising and provide the basis for further evaluation by quantitative real-time analysis in prospective clinical trials. For AML without a specific fusion transcript, the WT1 gene is an alternative molecular target. The clinical value of quantitative MRD monitoring in AML, however, will need to be confirmed in future studies.

Detection of minimal residual disease

A high percentage of patients with leukemia, lymphoma, and solid tumors achieve a complete clinical remission after initial treatment, but the majority of these patients will finally relapse from residual tumor cells detectable in clinical remission only by the most sensitive methods. The in vitro amplification of tumor-specific DNA or RNA sequences by polymerase chain reaction (PCR) allows identification of a few neoplastic cells in 10(4) to 10(6) normal cells. Depending on the underlying malignant disease and therapeutic treatment, the presence of residual tumor cells in an individual patient may herald relapse, but a long-term stable situation or slowly vanishing tumor cells are also possible. Molecular monitoring of residual leukemia and lymphoma cells by quantitative PCR techniques has provided important information about the effectiveness of treatment and the risk of recurrent disease as shown by minimal residual disease (MRD) analysis in patients with various malignant diseases. Such diseases include childhood acute lymphoblastic leukemia, after induction therapy; acute promyelocytic leukemia, during and after chemotherapy; and chronic myelogenous leukemia, during treatment with alpha-interferon and after allogeneic bone marrow transplantation. Evaluation of the predictive value of the detection of MRD has to take into account its evolution and course, the pathogenesis, biology, and natural course of the underlying malignant disease, the molecular genetic lesion, and finally, the type of treatment. Quantification of minimal residual cells by the recently developed real-time quantitative PCR technique will surely have a major impact on our therapeutic strategies for patients with leukemia, lymphomas, and solid tumors. Based on quantitative PCR data, the terms molecular remission and molecular relapse have to be exactly defined and validated in prospective clinical trials to assess the biological and clinical significance of MRD in various types of malignancies.

Quantitative detection of AML1-ETO rearrangement by real-time RT-PCR using fluorescently labeled probes

The persistence of the AML1-ETO rearrangement performed by reverse transcription polymerase chain reaction (RT-PCR) has been reported in acute myeloid leukemia (AML) patients in long-term complete remission (CR). This persistence, which is not associated with hematological relapse, limits the clinical use of qualitative RT-PCR. Here, we present a new quantitative real-time PCR method to detect AML1-ETO rearrangement using fluorescently labeled probes. Quantitative detection of AML1-ETO was performed in capillary tubes using two fluorescently labeled probes in the LightCycler equipment. The reliability of the method was checked in twenty-two bone marrow samples and one apheresis sample from eight patients with t(8;21) collected at diagnosis and during follow-up assessment. The regression coefficients obtained for standard curves of AML1-ETO and AML were all greater than 0.98. The sensitivity attained allowed the detection of rearrangements at a dilution of 10(-5) Kasumi-1 cDNA. The intra-assay coefficient of variation was 4% for AML1-ETO, and 7% for AML. The inter-assay coefficient of variation was 19% for AML1-ETO and 12% for AML. A log reduction from two to four in the AML1-ETO/AML ratio was evident after CR. The study of the method and first results obtained in patient samples support that quantitative real-time PCR with hybridization probes is a new reliable and sensitive method to monitor minimal residual disease in AML patients. Moreover, the fluorescent probes with the Light-Cycler technology offer the advantage of a rapid detection.

Minimal residual disease in leukaemia patients

Because of developments in diagnosis of haemopoietic malignant diseases during the past two decades, routine and reliable identification of very low numbers of malignant cells, known as minimal residual disease (MRD), is now possible. Several large-scale studies have shown that monitoring of MRD in haemopoietic malignant disease predicts clinical outcome. In acute lymphoblastic leukaemia, MRD detection is useful for evaluating early response to treatment and consequently for improving stratification, including treatment reduction. In acute promyelocytic leukaemia and chronic myeloid leukaemia, MRD information at specific time points enables effective early treatment intervention. MRD monitoring is also possible in other leukaemia subtypes, but in these disorders the clinical value of MRD detection is not yet known.

Monitoring of minimal residual disease in children with acute promyelocytic leukemia by RT-PCR detecting PML/RARalpha chimeric gene: a retrospective study of clinical feasibility

We studied retrospectively the clinical feasibility of minimal residual disease (MRD) monitoring by reverse transcription-polymerase chain reaction (RT-PCR) detecting the PML/retinoic acid receptor alpha (RARalpha) chimeric gene in children with acute promyelocytic leukemia (APL). MRD monitoring of APL was performed with standard and nested RT-PCR for PML/RARalpha gene, the sensitivity of which was 1 leukemic cell in 10(3)-10(4) and 1 in 10(4)-10(5) cells, respectively. Patients were nine children with APL (average age: 8.3 year; average period of follow-up: 69.2 months) who, after achieving remission with all-trans retinoic acid (ATRA), received treatment either with multidrug chemotherapy or with a combination of chemotherapy and ATRA. Out of six patients treated with multidrug-combined chemotherapy, two patients exhibited PCR positivity after six months of post- remission therapy, which shifted from the detectable range of the nested PCR to that of the standard PCR. These two patients subsequently relapsed and, together with two of the other patients receiving multidrug-combined chemotherapy, underwent allogeneic bone marrow transplantation. No MRD was detected in these patients after transplantation. In the remaining three patients who underwent cyclic treatment with alternative chemotherapy and ATRA, two showed positive RT-PCR at the nested or standard level, respectively, after six months of combined therapy, and one of them relapsed. Overall, three of four patients with MRD detected in post-remission period ultimately relapsed, while all of five patients without detectable MRD had a good prognosis. These findings suggest that impending relapse may be predicted by the detection of preceding PCR positivity with an increasing quantity of the PML/RARalpha mRNA that appears beyond six months of post-remission chemotherapy, with or without combined ATRA therapy.

The molecular genetics of recurring chromosome abnormalities in acute myeloid leukemia

Chromosome translocations are closely associated with a particular morphologic or phenotypic subtype of acute myeloid leukemia (AML). Cloning the genes at the breakpoints of these rearrangements has had a major impact on our understanding of the molecular biology of AML. Thus, cytogenetic or direct molecular genetic methods have become an essential part of the routine diagnostic evaluation and follow-up of AML patients. This review describes the MLL gene on 11q23 including three types of t(10;11), the TLS/FUS gene on 21q22, the AML1 gene on 21q22, and the NUP98 gene on 11p15. The target gene(s) of MLL is unknown at present, but it appears to be involved in maintaining function of some of the homeobox genes. The transcriptional coactivators, CBP and p300, were found to be involved in leukemogenesis through translocations. Characterization of the functions of genes involved in these translocations has enriched our understanding of their roles in leukemogenesis, and provided some suggestions for new therapy.

Quantitation of minimal residual disease in t(8;21)-positive acute myelogenous leukemia patients using real-time quantitative RT-PCR

t(8;21) is one of the common chromosomal translocations in acute myelogenous leukemia (AML). Using a recently developed real-time quantitative polymerase chain reaction (PCR) system, we analyzed the minimal residual disease (MRD) in bone marrow samples from seven AML patients with t(8;21) at different time points during the clinical courses of their disease. Four of these patients received chemotherapy and allogenic bone marrow transplantation (allo-BMT), and the other three were treated with chemotherapy alone. Two of the patients that received allo-BMT suffered a relapse. In these patients, the levels of AML1-MTG8 mRNA expression were shown to quantitatively increase. After re-induction chemotherapy and donor lymphocyte infusion therapy, AML went into remission and the expression levels decreased. In the other two patients receiving allo-BMT, the disease went into remission and the level of AML1-MTG8 mRNA expression remained under the detectable range. The other three patients received several courses of chemotherapy, without allo-BMT, and all of them clinically reached the hematological and cytogenetic remission state. However, there were low but detectable levels of MRD in their bone marrow samples. These results suggest that the real-time quantitative PCR assay is very useful for the monitoring of MRD and detecting an early relapse. This assay may also be useful in determining the quantitative difference in myelo-ablative activity between the chemotherapy alone and chemotherapy in conjunction with allo-BMT.

Molecular quantitation of minimal residual disease in acute myeloid leukemia with t(8;21) can identify patients in durable remission and predict clinical relapse

One of the most common translocations in acute myeloid leukemia (AML) is the t(8;21), which produces the fusion gene AML1-MTG8. We have developed a sensitive competitive reverse transcriptase-polymerase chain reaction (RT-PCR) assay forAML1-MTG8 transcripts, coupled with a competitive RT-PCR for the ABL transcript as a control to accurately estimate the level of amplifiable RNA. We have shown that AML1-MTG8 andABL transcripts have equal degradation rates. Thus, this method is useful for multicenter studies. We studied 25 patients with t(8;21) AML by means of serial analysis done on bone marrow (BM) and peripheral blood (PB) samples from 21 patients. Our analysis showed that, in general, a successful induction chemotherapy produces a reduction of 2 to 3 log in the level of AML1-MTG8, followed by a further 2 to 3 log after consolidation/intensification chemotherapy. Levels up to 1 × 103 and 1 × 102 molecules/μg of RNA in BM and PB, respectively, were compatible with durable remission. On the other hand, 5 patients with levels of 0.71 × 105to 2.27 × 105 molecules/μg of RNA in BM and 2.27 × 103 to 2.27 × 104 molecules/μg of RNA in PB had hematologic relapse within 3 to 6 months. Our data indicate that serial quantitation of AML1-MTG8 transcripts is useful in identifying patients at high risk of relapse and may offer an opportunity for clinical intervention to prevent hematologic relapse. This approach was applied successfully in a patient who had an allogeneic BM transplantation. We also suggest that PB may be used an alternative to BM for quantitating AML1-MTG8 transcripts.

Evaluation of minimal residual disease using reverse-transcription polymerase chain reaction in t(8;21) acute myeloid leukemia: a multicenter study of 51 patients

PURPOSE

Most studies using various reverse-transcription polymerase chain reaction (RT-PCR) techniques reported that the detection of the AML1-ETO fusion transcript was a common finding in long-term complete remission (CR) in acute myeloid leukemia (AML) with t(8;21) translocation. However, larger prospective studies with interlaboratory quality control may be important to investigate more precisely the clinical usefulness of studying minimal residual disease with RT-PCR in t(8;21) AML.

PATIENTS AND METHODS

We collected 223 marrow samples from 51 patients with t(8;21) AML diagnosed in five centers and tested all samples by two different RT-PCR techniques (a nested technique and a one-step technique, with a sensitivity of 10(-6) and 10(-5), respectively) in two different laboratories.

RESULTS

Samples from 14 patients in long persistent CR (median follow-up duration, 112 months) were taken at least twice, and all were PCR-negative by both techniques. Samples were prospectively taken from 37 patients after achievement of first CR and/or second CR, before intensive consolidation treatment, and every 3 to 6 months after completion of therapy. Patients who converted to PCR negativity with the one-step technique (60%) or both techniques (48%) after CR achievement had a longer CR duration than those with persistently positive PCR results (two-sided log-rank test, P =.0001). Patients who became PCR-negative with the one-step technique before intensive consolidation (23%) had a lower relapse rate (11% v 72%) and a longer CR duration than those who remained persistently PCR-positive at that point (two-sided log-rank test, P =.0015).

CONCLUSION

Patients with AML with t(8;21) in long-term remission were all PCR-negative. In prospectively studied patients, a good correlation was found between negative PCR results and absence of relapse. Early negative results with the one-step RT-PCR technique, before consolidation treatment, seemed to carry an especially good prognosis, suggesting that RT-PCR analysis could help in choosing the type of consolidation therapy in patients with t(8;21) AML.

Mixed-lineage leukemia with t(10;11)(p13;q21): an analysis of AF10-CALM and CALM-AF10 fusion mRNAs and clinical features

A fusion transcript of AF10 and CALM was isolated recently from the U937 cell line with t(10;11)(p13;q21). We performed reverse transcription-polymerase chain reaction and sequencing analysis on the t(10;11) leukemia samples obtained from four patients and one cell line, and we identified reciprocal fusion transcripts of AF10 and CALM in all the samples. The fusion transcripts in the five samples showed four different breakpoints in AF10 and three different breakpoints in CALM. In addition, the fusion transcripts in one sample showed a nucleotide sequence deletion in AF10, and those in two samples showed a nucleotide sequence deletion in CALM; the deletions were thought to be caused by alternative splicing. The variety of breakpoints and splice sites in the two genes resulted in five different-sized AF10-CALM mRNAs and in four different-sized CALM-AF10 mRNAs. Clinical features of 11 patients, including 6 of our own and 5 reported by others, in whom the fusion of AF10 and CALM was identified, are characterized by young age of the patients, mixed-lineage immunophenotype with coexpression of T-cell and myeloid antigens, frequent occurrence of a mediastinal mass, and poor clinical outcome.

Detection of residual disease in acute lymphoblastic leukemia of childhood

Several techniques developed in recent years provide us with the capability to detect sub-microscopic leukemia during remission. Quantitative polymerase chain reaction (PCR) is thus far the most sensitive assay that is applicable in most patients with acute lymphoblastic leukemia (ALL) of childhood. However, false-positive and false-negative results may provide the clinician with misleading data and therefore PCR analysis should be accompanied by another assay and changes in the level of residual disease should be confirmed at different time points following treatment. Furthermore, several studies did not determine a threshold of residual disease level above which relapse is likely to occur, and more recent data show that long-term remission may be sustained in the presence of residual disease. Thus, additional studies of the biology of residual disease in childhood ALL should be performed before sensitive assays of residual disease detection and quantitation can be clinically utilized.

Disappearance of AML1-MTG8 transcript by reverse transcriptase polymerase chain reaction in a patient in remission of acute myeloid leukemia (M2) after low-dose cytosine arabinoside

It is well-known that low dose cytosine arabinoside (LDAC) has activity in elderly patients with acute myeloid leukemia (AML). Several studies have shown that AML patients with t(8;21) in long term complete remission (CR) following intensive chemotherapy or allogeneic bone marrow transplantation (BMT) still have persistence of AML1-MTG8 transcripts by reverse transcriptase polymerase chain reaction (RT-PCR) method. We report here a patient who has no evidence of residual disease detectable by RT-PCR after LDAC. A 69-year-old patient did not obtain CR after two courses of intensive chemotherapy with behenoyl-ara-C, daunorubicin, 6-mercaptopurine and prednisolone. He received subcutaneous LDAC 10 mg every 12 h and granulocyte colony-stimulating factor (G-CSF) for 29 days and achieved CR. He continued on a 21 to 28-day course of LDAC without G-CSF every 2 or 3 months and has remained well and in CR for 5 years without chimeric AMLI-MTG8 transcript by RT-PCR. LDAC therapy seems to be effective in eradicating the leukemic clone as post-induction or maintenance therapy in this patient. This is the first case report of the disappearance of AML1-MTG8 transcript by RT-PCR in a patient with t(8;21) in long-term remission after LDAC.

Abnormalities of the FHIT transcripts in osteosarcoma and Ewing sarcoma

In a study of FHIT gene abnormalities by reverse transcription-polymerase chain reaction (RT-PCR) and sequence analysis of the PCR products, we found normal and abnormal PCR products in 11 osteosarcomas, one osteosarcoma cell line and 3 Ewing sarcomas, and a normal PCR product only in 5 osteosarcomas and 8 Ewing sarcomas. Sequence analysis of the abnormal PCR products revealed 7 osteosarcomas lacking exons 4 to 6, 7, 8 or 9, two lacking exons 5 to 7 or 10, and two lacking exons 6 to 8 or 10. In the aberrant transcripts of the 11 osteosarcomas, fusion had occurred in the exon/intron junctions in 2 tumors, between a segment within an exon and a complete exon in 3, and between segments within exons in 6. The 3 Ewing sarcomas had lost exon 4 or 5 to exon 6 or 10, and fusion had occurred in the exon/intron junction in one, and between segments within exons in 2. These findings suggest that both abnormal or variant splicing and other mechanisms such as genomic instabilities in the FHIT locus may have resulted in the expression of aberrant transcripts. One osteosarcoma and one cell line established from this osteosarcoma showed different abnormal FHIT transcripts, indicating that the tumor cells with the initial aberrant transcripts may not have had a selective advantage for proliferation. The FHIT abnormalities did not seem to be correlated with lung metastasis or a poor clinical outcome in our patients with osteosarcoma or Ewing sarcoma.

Molecular monitoring of minimal residual disease in acute myeloblastic leukemia with t(8;21) by RT-PCR

The t(8;21) is one of the most common translocations in acute myeloid leukaemia (AML) occurring in approximately 20% of adult and 40% of paediatric AML-M2. This translocation fuses the AML1 gene on chromosome 21q to the MTG8 (ETO) gene on chromosome 8q to produce the fusion gene AML1-MTG8. Transcripts for the AML1-MTG8 fusion gene have been detected in the majority of patients in remission by qualitative RT-PCR methods. Thus for such patients these methods are unsuitable for monitoring minimal residual disease (MRD). Furthermore, the diverse form of transcripts for this fusion gene was found in patients at different phases of their disease, which rules out the usefulness of the expression of any particular set of transcripts as a marker for monitoring MRD in those patients. On the other hand a quantitative RT-PCR method we developed, was able to assess the effectiveness of treatment and predict relapse up to four months before the onset of haematological relapse. This method should distinguish patients in stable remission from those at high risk of relapse and therefore identify patients who would require additional or new treatment such as BMT.

Comparison of two reverse transcription-polymerase chain reaction methods for detection of AML1/ETO rearrangement in the M2 subtype of acute myeloid leukaemia

Two reverse transcription-polymerase chain reaction methods to detect the AML1/ETO rearrangement in the M2 subtype of acute myeloid leukaemia those of Downing et al. (Blood 1993; 81: 2860-5) and Satake et al. (Br J Haematol 1995; 91: 892-8) were evaluated. Bone marrow samples, one at diagnosis and two in complete remission from a patient with M2 subtype of acute myeloid leukaemia, with t(8;21), were analysed using both methods. The Kasumi-1 cell line was used as a positive control and a patient with M3 subtype of acute myeloid leukaemia as a negative control. To confirm the feasibility of Satake's method a group of 35 patients with subtypes of acute myeloid leukaemia at diagnosis were studied. The method of Downing requires Southern blotting and hybridization with a specific probe because it often generates non-specific amplification products. By contrast, the method of Satake yields only a single amplification product, using one single round of PCR in samples at diagnosis, or two rounds in complete remission samples. The sensitivity of this method allows the detection of a single Kasumi-1 cell in 10(6) normal cells. The AML1/ETO rearrangement was observed in 5 of the 35 cases of acute myeloid leukaemia at diagnosis (14.3%) and in 3 of the 14 cases of M2 subtype of acute myeloid leukaemia (21.4%). The two remaining positive cases corresponded to the acute myeloid leukaemia subtypes M4 and M6. The results indicate that the method of Satake better meets the requirements of the clinical laboratory due to its greater simplicity, specificity, sensitivity and feasibility, thus making it more appropriate for use in diagnosing and monitoring minimal residual disease.

Minimal residual disease in acute monocytic leukemia patient with trisomy 11 and partial tandem duplication of MLL

We studied MLL rearrangements in five patients with myeloid hematologic malignancies with trisomy 11. Two had acute monocytic leukemia (AMoL), one had chronic myelomonocytic leukemia, one had refractory anemia, and the other had juvenile chronic myelogenous leukemia. Only one patient, a 15-year-old boy with AMoL and simple trisomy 11, showed rearrangement of MLL. He did not respond to chemotherapy, and successfully underwent bone marrow transplantation, but suffered a relapse 22 months later. Reverse transcription-polymerase chain reaction (RT-PCR) and sequencing analyses of bone marrow cells revealed a tandem duplication of MLL, and his relapse was predictable by sequential RT-PCR studies before it was clinically evident. Of 16 acute myeloid leukemia patients with trisomy 11 and rearrangement of MLL reported, our patient was the youngest in age and the only one with AMoL.

Rapid disappearance of AML1/ETO fusion transcripts in patients with t(8;21) acute myeloid leukemia following bone marrow transplantation and chemotherapy

To assess the clinical significance of monitoring minimal residual disease in t(8;21)(q22;q22) AML, RT-PCR assay was conducted during the clinical course of 12 patients who had undergone BMT or conventional chemotherapy. Two cases relapsed after BMT and chimeric RNA was detected soon after BMT in their bone marrow cells. The other three cases, in whom chimeric RNA was not detected after BMT, are in CR at 21 to 33 months following BMT. Similarly, four out of 7 cases who showed negative chimeric RNA after completion of chemotherapy have been in CR at 11 to 34 months following completion of chemotherapy. The present findings appear different from other studies which reported the detection of AML1-ETO chimeric RNA in long-term CR patients.