Assessment of minimal residual disease (MRD) in CBFbeta/MYH11-positive acute myeloid leukemias by qualitative and quantitative RT-PCR amplification of fusion transcripts

The evolution of minimal residual disease: key insights based on a bibliometric visualization analysis from 2002 to 2022

Background

The topic of minimal residual disease (MRD) has emerged as a crucial subject matter in the domain of oncology in recent years. The detection and monitoring of MRD have become essential for the diagnosis, treatment, and prognosis of various types of malignancy.

Aims

The purpose of this study is to explore the research trends, hotspots, and frontiers of MRD in the last two decades through bibliometric analysis.

Methods

We employed Web of Science databases to carry out a bibliometric visualization analysis of research on 8,913 academic papers about MRD research from 2002 to 2022. VOSviewer, CiteSpace, RStudio, and a bibliometric online analysis platform were mainly used to conduct co-occurrence analysis and cooperative relationship analysis of countries/regions, institutions, journals, and authors in the literature. Furthermore, co-occurrence, co-citation, and burst analyses of keyword and reference were also conducted to generate relevant knowledge maps.

Results

In the past 20 years, the number of MRD research papers has presented an overall rising trend, going through three stages: a plateau, development, and an explosion. The output of articles in the United States was notably superior and plays a dominant role in this field, and the Netherlands had the highest average citation per article. The most productive and influential institution was the University of Texas MD Anderson Cancer Center. Blood published the most papers and was the most cited journal. A collection of leading academics has come to the fore in the research field, the most prolific of which is Kantarjian HM. It was found that the application of MRD in "acute myeloid leukemia", "acute lymphoblastic leukemia", "multiple myeloma", as well as the detection technology of MRD, are the research hotspots and frontiers in this domain. Furthermore, we analyzed the co-citation network of references and found that the top 10 co-cited references were all associated with MRD in hematological malignancies.

Conclusion

This bibliometric visualization analysis conducted a thorough exploration into the research hotspots and trends in MRD from 2002 to 2022. Our findings can aid researchers in recognizing possible collaborations, guiding future research directions, and fostering the growth of MRD detection and monitoring technologies.

Activity of decitabine as maintenance therapy in core binding factor acute myeloid leukemia

Background

Posttherapy measurable residual disease (MRD) positivity in core binding factor acute myeloid leukemia (CBF‐AML) is associated with shorter relapse‐free survival (RFS). Elimination of MRD measured via quantitative reverse transcription polymerase chain reaction (qRTPCR) for disease specific transcripts can potentially lead to better outcomes in CBF‐AML.

Methods

We prospectively monitored the MRD using qRTPCR and flow cytometry on bone marrow samples in patients with newly diagnosed CBF‐AML who received decitabine (DAC) maintenance therapy after fludarabine/cytarabine/G‐CSF (FLAG)‐based induction/consolidation regimen. Negative qRTPCR (CMR) was defined as fusion transcript <0.01%.

Results

Thirty‐one patients with CBF‐AML including 14 with t(8;21) and 17 with inv(16) received parenteral DAC as maintenance therapy. Fifteen patients (48.3%) had completed FLAG‐based induction/consolidation but with positive MRD (0.35%, range = 0.01%–0.91%) (Group 1). Sixteen patients (51.7%) could not complete recommended consolidations with FLAG‐based regimen (due to older age or complications) and were switched to DAC maintenance (Group 2). In Group 2, eight patients (50%) had undetectable MRD (Group 2A) (all had qRTPCR ≤ 0.01%) and the other eight patients (50%) had residual fusion product by qRTPCR (0.1%, range = 0.02%–0.36%) (Group 2B) prior to starting DAC. Amongst the 23 patients who had a PCR ≥ 0.01% before maintenance therapy (Groups 1 and 2B), 12 patients (52%) attained a CMR as their best response (responders). The median pre‐DAC qRTPCR amongst responders were 0.03% compared to 0.14% in nonresponders (p = .002). The median estimated molecular RFS amongst responders were 93.9 months. At a median follow‐up of 59.3 months (13.2–106 months) from DAC initiation, 16 patients (51.6%) had to be initiated on a second line of therapy (40%, 25%, and 100% patients, respectively, in Groups1, 2A, and 2B). The median estimated time to new treatment between responders was 112.4 versus 5.8 months in nonresponders (hazard ratio = 0.16, 95% confidence interval = 0.04–0.54); however, there were no difference in overall survival between these groups (p = .37).

Conclusion

DAC is an effective maintenance therapy for CBF‐AML patients with persistent fusion transcript at a low level after FLAG‐based regimen. Attainment of CMR with DAC maintenance can lead to long‐term remission in patients who have persistent MRD positive after FLAG‐based regimen or are unable to receive the full course of consolidation therapy.

Monitoring of post-transplant MLL-PTD as minimal residual disease can predict relapse after allogeneic HSCT in patients with acute myeloid leukemia and myelodysplastic syndrome

Background

The mixed-lineage leukemia (MLL) gene is located on chromosome 11q23. The MLL gene can be rearranged to generate partial tandem duplications (MLL-PTD), which occurs in about 5-10% of acute myeloid leukemia (AML) with a normal karyotype and in 5-6% of myelodysplastic syndrome (MDS) patients. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is currently one of the curative therapies available for AML and MDS with excess blasts (MDS-EB). However, how the prognosis of patients with high levels of MLL-PTD after allo-HSCT, and whether MLL-PTD could be used as a reliable indicator for minimal residual disease (MRD) monitoring in transplant patients remains unknown. Our study purposed to analyze the dynamic changes of MLL-PTD peri-transplantation and the best threshold for predicting relapse after transplantation.

Methods

We retrospectively collected the clinical data of 48 patients with MLL-PTD AML or MDS-EB who underwent allo-HSCT in Peking University People’s Hospital. The MLL-PTD was examined by real-time quantitative polymerase chain reaction (RQ-PCR) at the diagnosis, before transplantation and the fixed time points after transplantation. Detectable MLL-PTD/ABL > 0.08% was defined as MLL-PTD positive in this study.

Results

The 48 patients included 33 AML patients and 15 MDS-EB patients. The median follow-up time was 26(0.7-56) months after HSCT. In AML patients, 7 patients (21.2%) died of treatment-related mortality (TRM), 6 patients (18.2%) underwent hematological relapse and died ultimately. Of the 15 patients with MDS-EB, 2 patients (13.3%) died of infection. The 3-year cumulative incidence of relapse (CIR), overall survival (OS), disease-free survival (DFS) and TRM were 13.7 ± 5.2, 67.8 ± 6.9, 68.1 ± 6.8 and 20.3% ± 6.1%, respectively. ROC curve showed that post-transplant MLL-PTD ≥ 1.0% was the optimal cut-off value for predicting hematological relapse after allo-HSCT. There was statistical difference between post-transplant MLL-PTD ≥ 1.0% and MLL-PTD < 1.0% groups (3-year CIR: 75% ± 15.3% vs. 0%, P < 0.001; 3-year OS: 25.0 ± 15.3% vs. 80.7% ± 6.6%, P < 0.001; 3-year DFS: 25.0 ± 15.3% vs. 80.7 ± 6.6%, P < 0.001; 3-year TRM: 0 vs. 19.3 ± 6.6%, P = 0.277). However, whether MLL-PTD ≥ 1% or MLL-PTD < 1% before transplantation has no significant difference on the prognosis.

Conclusions

Our study indicated that MLL-PTD had a certain stability and could effectively reflect the change of tumor burden. The expression level of MLL-PTD after transplantation can serve as an effective indicator for predicting relapse.

Dynamic assessment of measurable residual disease in favorable-risk acute myeloid leukemia in first remission, treatment, and outcomes

We aimed to investigate outcomes of different post-remission treatment (PRT) choices based on dynamic measurable residual disease (MRD) by multiparameter flow cytometry in favorable-risk AML (FR-AML). Four hundred and three younger patients with FR-AML in first complete remission (CR1) were enrolled in this registry-based cohort study, including 173 who received chemotherapy (CMT), 92 autologous stem cell transplantation (auto-SCT), and 138 allogeneic SCT (allo-SCT). The primary endpoint was the 5-year overall survival (OS). Subgroup analyses were performed based on dynamic MRD after the 1st, 2nd, and 3rd courses of chemotherapy. In subgroups of patients with negative MRD after 1 or 2 course of chemotherapy, comparable OS was observed among the CMT, auto-SCT, and allo-SCT groups (p = 0.340; p = 0.627, respectively). But CMT and auto-SCT had better graft-versus-host-disease-free, relapse-free survival (GRFS) than allo-SCT in both subgroups. For patients with negative MRD after three courses of chemotherapy, allo-SCT had better disease-free-survival than CMT (p = 0.009). However, OS was comparable among the three groups (p = 0.656). For patients with persistently positive MRD after 3 courses of chemotherapy or recurrent MRD, allo-SCT had better OS than CMT and auto-SCT (p = 0.011; p = 0.029, respectively). Dynamic MRD might improve therapy stratification and optimize PRT selection for FR-AML in CR1.

How to Improve Prognostication in Acute Myeloid Leukemia with CBFB-MYH11 Fusion Transcript: Focus on the Role of Molecular Measurable Residual Disease (MRD) Monitoring

Acute myeloid leukemia (AML) carrying inv(16)/t(16;16), resulting in fusion transcript CBFB-MYH11, belongs to the favorable-risk category. However, even if most patients obtain morphological complete remission after induction, approximately 30% of cases eventually relapse. While well-established clinical features and concomitant cytogenetic/molecular lesions have been recognized to be relevant to predict prognosis at disease onset, the independent prognostic impact of measurable residual disease (MRD) monitoring by quantitative real-time reverse transcriptase polymerase chain reaction (qRT-PCR), mainly in predicting relapse, actually supersedes other prognostic factors. Although the ELN Working Party recently indicated that patients affected with CBFB-MYH11 AML should have MRD assessment at informative clinical timepoints, at least after two cycles of intensive chemotherapy and after the end of treatment, several controversies could be raised, especially on the frequency of subsequent serial monitoring, the most significant MRD thresholds (most commonly 0.1%) and on the best source to be analyzed, namely, bone marrow or peripheral blood samples. Moreover, persisting low-level MRD positivity at the end of treatment is relatively common and not predictive of relapse, provided that transcript levels remain stably below specific thresholds. Rising MRD levels suggestive of molecular relapse/progression should thus be confirmed in subsequent samples. Further prospective studies would be required to optimize post-remission monitoring and to define effective MRD-based therapeutic strategies.

Eradication of Measurable Residual Disease in AML: A Challenging Clinical Goal

In non-promyelocytic (non-M3) AML measurable residual disease (MRD) detected by multi-parameter flow cytometry and molecular technologies, which are guided by Consensus-based guidelines and discover very low leukemic cell numbers far below the 5% threshold of morphological assessment, has emerged as the most relevant predictor of clinical outcome. Currently, it is well-established that MRD positivity after standard induction and consolidation chemotherapy, as well as during the period preceding an allogeneic hematopoietic stem cell transplant (allo-HSCT), portends to a significantly inferior relapse-free survival (RFS) and overall survival (OS). In addition, it has become absolutely clear that conversion from an MRD-positive to an MRD-negative state provides a favorable clinical outcome similar to that associated with early MRD negativity. Thus, the complete eradication of MRD, i.e., the clearance of the few leukemic stem cells-which, due to their chemo-radiotherapy resistance, might eventually be responsible of disease recurrence-has become an un-met clinical need in AML. Nowadays, this goal might potentially be achieved thanks to the development of novel innovative treatment strategies, including those targeting driver mutations, apoptosis, methylation patterns and leukemic proteins. The aim of this review is to analyze these strategies and to suggest any potential combination able to induce MRD negativity in the pre- and post-HSCT period.

Peripheral blood molecular measurable residual disease is sufficient to identify patients with acute myeloid leukaemia with imminent clinical relapse

Longitudinal molecular measurable residual disease (MRD) sampling after completion of therapy serves as a refined tool for identification of imminent relapse of acute myeloid leukaemia (AML) among patients in long-term haematological complete remission. Tracking of increasing quantitative polymerase chain reaction MRD before cytomorphological reappearance of blasts may instigate individual management decisions and has paved the way for development of pre-emptive treatment strategies to substantially delay or perhaps even revert leukaemic regrowth. Traditionally, MRD monitoring is performed using repeated bone marrow aspirations, albeit the current European LeukemiaNet MRD recommendations acknowledge the use of peripheral blood as an alternative source for MRD assessment. Persistent MRD positivity in the bone marrow despite continuous morphological remission is frequent in both core binding factor leukaemias and nucleophosmin 1-mutated AML. In contrast, monthly assessment of MRD in peripheral blood superiorly separates patients with imminent haematological relapse from long-term remitters and may allow pre-emptive therapy of AML relapse.

The loss or absence of minimal residual disease of <0·1% at any time after two cycles of consolidation chemotherapy in CBFB-MYH11-positive acute myeloid leukaemia indicates poor prognosis

No consensus has been reached on the relationship between CBFB-MYH11 copies and prognosis. Of 1525 acute myeloid leukemia (AML) patients, 58 with CBFB-MYH11-positive AML (16/58 patients with c-kit mutation) were retrospectively analyzed with a median follow-up duration of 29.8 (range: 4.8-74.4) months. Of these, 25/58 (43.1%) patients underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT), 10 of whom had the c-kit mutation. Of the 33 patients who did not undergo allo-HSCT, recurrence in patients with CBFB-MYH11/ABL level >0.1% at any time after two consolidation cycles was significantly higher than in patients with CBFB-MYH11/ABL level <0.1% (61.9% vs. 0%, P = 0.001); further, the 3-year relapse-free survival (RFS; 31.4% vs. 100%, P = 0.004) and event-free survival (EFS; 33.1% vs. 100%, P = 0.004) were significantly decreased in patients with CBFB-MYH11/ABL level >0.1% at any time after two consolidation cycles. The 3-year RFS and EFS rates were lower in patients who did not receive allo-HSCT than in those who did (31.4% vs 84.6%, P = 0.000; 31.4% vs. 80.8%, P = 0.001). CBFB-MYH11-positive AML patients with CBFB-MYH11/ABL level >0.1% at any time after two cycles of consolidation had poor prognoses, and allo-HSCT could improve their survival.

Role of minimal residual disease in the management of acute myeloid leukemia-a case-based discussion

AML is stratified into risk-categories based on cytogenetic and molecular features that prognosticate survival and facilitate treatment algorithms, though there is still significant heterogeneity within risk groupings with regard to risk of relapse and prognosis. The ambiguity regarding prognosis is due in large part to the relatively outdated criteria used to determine response to therapy. Whereas risk assessment has evolved to adopt cytogenetic and molecular profiling, response criteria are still largely determined by bone marrow morphologic assessment and peripheral cell count recovery. Minimal residual disease refers to the detection of a persistent population of leukemic cells below the threshold for morphologic CR determination. MRD assessment represents standard of care for ALL and PML, but concerns over prognostic capability and standardization have limited its use in AML. However, recent advancements in MRD assessment and research supporting the use of MRD assessment in AML require the reconsideration and review of this clinical tool in this disease entity. This review article will first compare and contrast the major modalities used to assess MRD in AML, such as RQ-PCR and flow cytometry, as well as touching upon newer technologies such as next-generation sequencing and digital droplet PCR. The majority of the article will discuss the evidence supporting the use of MRD assessment to prognosticate disease at various time points during treatment, and review the limited number of studies that have incorporated MRD assessment into novel treatment algorithms for AML. The article concludes by discussing the current major limitations to the implementation of MRD assessment in this disease. The manuscript is bookended by a clinical vignette that highlights the need for further research and refinement of this clinical tool.

Gene mutational pattern and expression level in 560 acute myeloid leukemia patients and their clinical relevance

Background

Cytogenetic aberrations and gene mutations have long been regarded as independent prognostic markers in AML, both of which can lead to misexpression of some key genes related to hematopoiesis. It is believed that the expression level of the key genes is associated with the treatment outcome of AML.

Methods

In this study, we analyzed the clinical features and molecular aberrations of 560 newly diagnosed non-M3 AML patients, including mutational status of CEBPA, NPM1, FLT3, C-KIT, NRAS, WT1, DNMT3A, MLL-PTD and IDH1/2, as well as expression levels of MECOM, ERG, GATA2, WT1, BAALC, MEIS1 and SPI1.

Results

Certain gene expression levels were associated with the cytogenetic aberration of the disease, especially for MECOM, MEIS1 and BAALC. FLT3, C-KIT and NRAS mutations contained conversed expression profile regarding MEIS1, WT1, GATA2 and BAALC expression, respectively. FLT3, DNMT3A, NPM1 and biallelic CEBPA represented the mutations associated with the prognosis of AML in our group. Higher MECOM and MEIS1 gene expression levels showed a significant impact on complete remission (CR) rate, disease free survival (DFS) and overall survival (OS) both in univariate and multivariate analysis, respectively; and an additive effect could be observed. By systematically integrating gene mutational status results and gene expression profile, we could establish a more refined system to precisely subdivide AML patients into distinct prognostic groups.

Conclusions

Gene expression abnormalities contained important biological and clinical informations, and could be integrated into current AML stratification system.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1279-4) contains supplementary material, which is available to authorized users.

Enhancing acute myeloid leukemia therapy - monitoring response using residual disease testing as a guide to therapeutic decision-making

INTRODUCTION

Current standards for monitoring the response of acute myeloid leukemia (AML) are based on morphologic assessments of the bone marrow and recovery of peripheral blood counts. A growing experience is being developed to enhance the detection of small amounts of AML, or minimal residual disease (MRD). Areas covered: Available techniques include multi-color flow cytometry (MFC) of leukemia associated immunophenotypes (LAIP), quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) for detecting fusion and mutated genes (RUNX1-RUNX1T1, CBFB-MYH11, and NPM1), overexpression of genes such as WT1, and next generation sequencing (NGS) for MRD. Expert commentary: While MRD monitoring is standard of care in some leukemia subsets such as acute promyelocytic leukemia, this approach for the broader AML population does not universally predict outcomes as some patients may experience relapse in the setting of undetectable leukemia while others show no obvious disease progression despite MRD positivity. However, there are instances where MRD can identify patients at increased risk for relapse that may change recommended therapy. Currently, prospective investigations to define clinically relevant MRD thresholds are ongoing. Risk-adapted trials are needed to best define the use of MRD in the follow up of AML patients after initial induction therapy.

Understanding the Clinical Implications of Minimal Residual Disease in Childhood Leukemia

Improved laboratory techniques now allow a more sensitive detection of leukemia cells at designated intervals throughout therapy. Using flow cytometry and polymerase chain reaction, it is possible to detect 1 leukemic cell among 10 4 normal cells (1 leukemia cell in 10,000 normal cells), representing a 100-fold greater sensitivity than morphological examination in acute lymphoblastic leukemia (ALL). Recently, it has been shown that the molecular presence of persistent acute lymphoblastic leukemia at the end of remission therapy is a poor indicator of clinical outcome. Now similar studies are being performed in acute myeloid leukemia (AML). While the sensitivity using flow cytometry is less in AML than in ALL (able to detect 1 leukemic cell among 1000 normal cells in AML), persistent or minimal residual AML provides the clinician guidance with future treatment recommendations. Minimal residual disease (MRD) is now considered an important indicator response of disease response to treatment. As such, MRD once considered a research variable is now influencing treatment decisions. Therefore, it is imperative that the nurse have an understanding of the newer techniques to study residual leukemia and their clinical implications for patients and their families.

Comparison of Multiparameter Flow Cytometry Immunophenotypic Analysis and Quantitative RT-PCR for the Detection of Minimal Residual Disease of Core Binding Factor Acute Myeloid Leukemia

OBJECTIVES

To examine the value of minimal residual disease (MRD) by multiparameter flow cytometry (MFC) in core binding factor (CBF) acute myeloid leukemia (AML).

METHODS

We studied 42 patients with t(8;21)(q22;q22)/RUNX1-RUNX1T1 and 51 with inv(16)(p13.1q22)/CBFB-MYH11 Tandem MRD analyses by MFC and quantitative reverse transcription polymerase chain reaction (qRT-PCR) were performed in 281 bone marrow (BM) samples.

RESULTS

Grouping qRT-PCR levels as ≤0.01, 0.01 to 0.1, 0.1 to 1, 1 to 10, and >10%, and reporting MFC (sensitivity, 0.1%-0.01%) as positive or negative, κ coefficient test showed no agreement between qRT-PCR and MFC in BM samples obtained postinduction (n = 44, κ = 0.041), and only weak agreement during consolidation (n = 108, κ = 0.083), maintenance/follow-up (n = 107, κ = 0.164), and salvage chemotherapy (n = 24, 0.376). In the post induction BM samples, while qRT-PCR <0.1% was associated with lower and ≥10% with higher AML relapse risk (P = .035), qRT-PCR between 0.1% to 1% and 1% to 10% failed to predict relapse. In the latter group with intermediate qRT-PCR results, MFC provided prognostic value for relapse (P = 0.006).

CONCLUSIONS

MFC and qRT-PCR are complementary tests in monitoring CBF AML MRD.

The clinical significance of negative flow cytometry immunophenotypic results in a morphologically scored positive bone marrow in patients following treatment for acute myeloid leukemia

In a patient with acute myeloid leukemia (AML) following therapy, finding ≥5% bone marrow (BM) blasts is highly concerning for residual/relapsed disease. Over an 18-month period, we performed multicolor flow cytometry immunophenotyping (MFC) for AML minimal residual disease on >4,000 BM samples, and identified 41 patients who had ≥5% myeloblasts by morphology but negative by MFC. At the time of a negative MFC study, an abnormal cytogenetic study converted to negative in 14 patients and remained positive at a low level (2.5-9.5%) by fluorescence in situ hybridization in 3 (14%), of the latter, abnormalities subsequently disappeared in the repeated BM in 2 patients. Positive pretreatment mutations, including FLT3, NPM1, IDH1, CEBPA, became negative in all 10 patients tested. Of the seven patients with favorable cytogenetics, PML/RARA, CBFB-MYH11 or RUNX1-RUNX1T1 fusion transcripts were detected at various levels in six patients but all patients remained in complete remission. With no additional chemotherapy given, 39 patients had BM repeated (median 2 weeks, range <1-21), and all cases showed <5% BM blasts and a continuously negative MFC. In the end of follow-up (median 10 months, range 1-22), 13 patients experienced relapse, 12/13 showing clonal cytogenetic evolution/switch and 11 demonstrating major immunophenotypic shifts. We conclude that MFC is useful in identifying a regenerating BM sample with ≥5% BM blasts that would otherwise be scored as positive using standard morphologic examination. We believe this conclusion is supported by the changes in molecular cytogenetic status and the patient clinical follow-up data.

Allogeneic stem cell transplant may improve the outcome of adult patients with inv(16) acute myeloid leukemia in first complete remission with poor molecular responses to chemotherapy

Eighty-six adult patients with inv(16) acute myeloid leukemia (AML) in first complete remission (CR1) were serially monitored for CBFB-MYH11 transcript levels during the early courses of chemotherapy. Fifty-seven and 29 of them received chemotherapy/autologous stem cell transplant (SCT) and allogeneic (allo-)SCT after second consolidation, respectively. For patients receiving chemotherapy/autologous SCT, the sole independent adverse prognostic factor for the cumulative incidence of relapse (CIR), disease-free survival (DFS) and overall survival (OS) was a CBFB-MYH11 level > 0.2% after course 2 consolidation (p = 0.003, 0.003 and 0.031), which was used to define a poor molecular response (MR). Allo-SCT significantly decreased the 3-year CIR and increased the DFS and OS of patients with a poor MR (p < 0.0001, 0.0001 and 0.045) but did not improve the outcome of patients with good MR (all p > 0.05) compared with chemotherapy/autologous SCT. Therefore, allo-SCT could improve the outcome of adult patients with inv(16) AML in CR1 with a poor MR during the early courses of chemotherapy.

Molecular methods used for detection of minimal residual disease following hematopoietic stem cell transplantation in myeloid disorders

The monitoring of minimal residual disease (MRD) in patients with acute or chronic myeloid disorders is performed routinely after allogeneic or autologous transplantation. The detection of MRD helps to identify patients who are at high risk for leukemic relapse after transplantation. The most commonly used techniques for MRD detection are qualitative and quantitative PCR methods, fluorescence in situ hybridization (FISH), fluorescence-activated cell sorting (FACS), and cytogenetic analysis, which are often performed complementary in order to assess more precisely MRD. Here we describe the most used sensitive real-time RT-PCR methods for chronic and acute myeloid disorders. Besides protocols for real-time RT-PCR and multiplex RT-PCR procedures for the most common fusion-gene transcripts in acute and chronic myeloid disorders, methods for detections of disease-specific genetic mutated alterations, as NPM1 and FLT3 gene length mutations, and aberrantly expressed genes, as WT1 gene transcripts, are described in detail for daily use.

Tumor heterogeneity makes AML a "moving target" for detection of residual disease

Detection of minimal residual disease is recognized as an important post-therapy risk factor in acute myeloid leukemia patients. Two most commonly used methods for residual disease monitoring are real-time quantitative polymerase chain reaction and multiparameter flow cytometry. The results so far are very promising, whereby it is likely that minimal residual disease results will enable to guide future post-remission treatment strategies. However, the leukemic clone may change between diagnosis and relapse due to the instability of the tumor cells. This instability may already be evident at diagnosis if different subpopulations of tumor cells coexist. Such tumor heterogeneity, which may be reflected by immunophenotypic, molecular, and/or cytogenetic changes, can have important consequences for minimal residual disease detection, since false-negative results can be expected to be the result of losses of aberrancies used as minimal residual disease markers. In this review the role of such changes in minimal residual disease monitoring is explored. Furthermore, possible causes of tumor instability are discussed, whereby the concept of clonal selection and expansion of a chemotherapy-resistant subpopulation is highlighted. Accordingly, detailed knowledge of the process of clonal evolution is required to improve both minimal residual disease risk stratification and patient outcome.

Serum peptidomic profiling identifies a minimal residual disease detection and prognostic biomarker for patients with acute leukemia

The evaluation of minimal residual disease (MRD) in acute leukemia (AL) is currently recognized as a potential critical tool to assess the response and relapse rate of treatments. The present study investigated serum peptides from patients with AL to identify biomarkers that would be useful in providing clinical evaluations and independent prognostic information. The patterns of serum peptides from 123 patients with AL and 49 healthy controls were analyzed using matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Furthermore, diagnostic models of differential peptides were established using the support vector machine (SVM) algorithm to discriminate between the AL patients and healthy controls or between the AL patients with various degrees of remission. Finally, the peptides were applied to evaluate the prognosis of the affected patients. The area under the receiver operating characteristic (ROC) curve (AUC), analyzed using the SVM algorithm to distinguish between the AL patients and healthy controls, was 0.921. The AUC of the models for distinguishing between the newly-diagnosed AL patients and those in AL-hematological complete remission (HCR) and between the AL-HCR patients from those in AL-molecular remission (MR), was 0.824 and 0.919, respectively. A short serum peptide of m/z 4625 was identified to decrease in density in parallel with an increase in the degree of remission, which was used to monitor the MRD level. The intensity of the m/z 4625 peptide was significantly correlated with a poor overall survival (OS). The m/z 4625 peptide was identified to be a partial fragment of SERPINA3. The serum peptide pattern is high in sensitivity and specificity and may be used to discriminate between AL patients with various degrees of remission. The m/z 4625 peptide may be used to monitor the MRD levels and provide independent prognostic information in patients with AL.

Comparative analysis of different approaches to measure treatment response in acute myeloid leukemia

PURPOSE

In acute myeloid leukemia (AML), initial treatment response by morphologic analysis of bone marrow predicts long-term outcome. Response can now be assessed by minimal residual disease (MRD) monitoring with flow cytometry or polymerase chain reaction (PCR). We determined the relation among the results of these approaches and their prognostic value.

PATIENTS AND METHODS

In the multicenter AML02 study, follow-up bone marrow samples from 203 children and adolescents with newly diagnosed AML were examined by flow cytometry (n = 1,514), morphology (n = 1,382), and PCR amplification of fusion transcripts (n = 508). Results were correlated with treatment outcome.

RESULTS

Among 1,215 samples with less than 5% leukemic myeloblasts by morphology, 100 (8.2%) were MRD positive (≥ 0.1%) by flow cytometry, whereas 96 (57.5%) of the 167 samples with ≥ 5% blasts were MRD negative. Virtually all (308 of 311; 99.0%) MRD-negative samples by PCR were also MRD negative by flow cytometry. However, only 19 (9.6%) of the 197 PCR-positive samples were flow cytometry positive, with analyses of AML1-ETO and CBFβ-MYH11 accounting for most discrepancies, whereas eight of 13 MLL-positive samples had detectable MRD by flow cytometry. MRD by flow cytometry after induction 1 or 2 predicted lower event-free survival and higher relapse rate (P < .001) and was an independent prognostic factor in a multivariable analysis; prediction was not improved by morphologic information or molecular findings.

CONCLUSION

In childhood AML, morphologic assessment of treatment response has limited value if MRD is measured by flow cytometry. MLL fusion transcripts can provide prognostic information in some patients, whereas monitoring of AML1-ETO and CBFβ-MYH11 transcripts is largely uninformative.

Minimal residual disease monitoring by quantitative RT-PCR in core binding factor AML allows risk stratification and predicts relapse: results of the United Kingdom MRC AML-15 trial

The clinical value of serial minimal residual disease (MRD) monitoring in core binding factor (CBF) acute myeloid leukemia (AML) by quantitative RT-PCR was prospectively assessed in 278 patients [163 with t(8;21) and 115 with inv(16)] entered in the United Kingdom MRC AML 15 trial. CBF transcripts were normalized to 10(5) ABL copies. At remission, after course 1 induction chemotherapy, a > 3 log reduction in RUNX1-RUNX1T1 transcripts in BM in t(8;21) patients and a > 10 CBFB-MYH11 copy number in peripheral blood (PB) in inv(16) patients were the most useful prognostic variables for relapse risk on multivariate analysis. MRD levels after consolidation (course 3) were also informative. During follow-up, cut-off MRD thresholds in BM and PB associated with a 100% relapse rate were identified: for t(8;21) patients BM > 500 copies, PB > 100 copies; for inv(16) patients, BM > 50 copies and PB > 10 copies. Rising MRD levels on serial monitoring accurately predicted hematologic relapse. During follow-up, PB sampling was equally informative as BM for MRD detection. We conclude that MRD monitoring by quantitative RT-PCR at specific time points in CBF AML allows identification of patients at high risk of relapse and could now be incorporated in clinical trials to evaluate the role of risk directed/preemptive therapy.

Development of plasmid calibrators for absolute quantification of miRNAs by using real-time qPCR

MicroRNAs (miRNAs) are small noncoding RNAs of approximately 18 to 25 nucleotides in length that negatively regulate gene expression via either the degradation or translational inhibition of their target mRNAs. Because miRNAs are essential for the regulation of critical physiological processes as well as a variety of pathological events, they have emerged as a novel class of molecular diagnostic biomarkers and therapeutic agents or targets. Accordingly, the need for novel methods for the quantification of miRNA has increased due to interest in their clinical implications. Currently, real-time quantitative polymerase chain reaction (qPCR) is considered the most robust technology for nucleic acid quantification. Different tools for miRNA quantification by using qPCR are now commercially available, but only relative quantification strategies have been reported. This situation may be partly due to the difficulty in obtaining an appropriate molecule with which to establish an miRNA calibration range. Here, we describe a rapid and convenient strategy for the development of a calibrator, which enables the absolute quantification of miRNAs by using qPCR and allows the cloning of a synthetic sequence of interest instead of a PCR product into a plasmid.

Prognostic Impact of Minimal Residual Disease inCBFB-MYH11–Positive Acute Myeloid Leukemia

Purpose

To evaluate the prognostic impact of minimal residual disease (MRD) in patients with acute myeloid leukemia (AML) expressing the CBFB-MYH11 fusion transcript.

Patients and Methods

Quantitative reverse transcriptase polymerase chain reaction (PCR) was performed on 684 bone marrow (BM; n = 331) and/or peripheral blood (PB; n = 353) samples (median, 13 samples per patient) from 53 younger adult (16 to 60 years old) patients with AML treated in prospective German-Austrian AML Study Group treatment trials. Samples were obtained at diagnosis (BM, n = 45; PB, n = 48), during treatment course (BM, n = 153; PB, n = 122), and at follow-up (BM, n = 133; PB, n = 183). To evaluate the applicability of PB for MRD detection, 198 paired BM and PB samples obtained at identical time points were analyzed.

Results

The following three clinically relevant checkpoints were identified during consolidation and early follow-up that predicted relapse: achievement of PCR negativity in at least one BM sample during consolidation therapy (2-year relapse-free survival [RFS], 79% v 54% for PCR positivity; P = .035); achievement of PCR negativity in at least two BM or PB samples during consolidation therapy and early follow-up (≤ 3 months; 2-year RFS, P = .001; overall survival, P = .01); and conversion from PCR negativity to PCR positivity with copy ratios of more than 10 after consolidation therapy. Analysis of paired BM and PB samples revealed BM samples to be more sensitive during the course of therapy, whereas for follow-up, PB samples were equally informative.

Conclusion

We defined clinically relevant MRD checkpoints that allow for the identification of patients with CBFB-MYH11–positive AML who are at high risk of relapse. Monitoring of CBFB-MYH11 transcript levels should be incorporated into future clinical trials to guide therapeutic decisions.

Acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous group of leukemias that result from clonal transformation of hematopoietic precursors through the acquisition of chromosomal rearrangements and multiple gene mutations. As a result of highly collaborative clinical research by pediatric cooperative cancer groups worldwide, disease-free survival has improved significantly during the past 3 decades. Further improvements in outcomes of children who have AML probably will reflect continued progress in understanding the biology of AML and the concomitant development of new molecularly targeted agents for use in combination with conventional chemotherapy drugs.

Minimal residual disease quantitation in acute myeloid leukemia

The prognosis for patients with acute myeloid leukemia (AML) is heterogeneous. A minority of patients have clinical and biologic features associated with a very high risk of relapse. For the remaining patients, no clear prognostic factors can be identified at diagnosis. The degree of treatment response is likely to be an informative predictor of outcome for these patients. Modern assays to detect AML cells that are undetectable by conventional morphologic techniques, ie, minimal residual disease (MRD), can potentially improve measurements of treatment response. It is plausible that modifications to treatment based on the results of these assays will improve clinical management and ultimately increase cure rates. Established MRD assays for AML are based on either polymerase chain reaction amplification of genetic abnormalities or flow cytometric detection of abnormal immunophenotypes. Residual disease and treatment response can be measured by these assays in a manner that is much more sensitive and objective than that afforded by conventional morphologic examination. The expanding use of MRD testing is beginning to change the definitions of treatment response and of remission. Other clinically informative uses of MRD testing include the detection of early relapse and the evaluation of the efficacy of new antileukemic agents.

Minimal residual disease levels assessed by NPM1 mutation-specific RQ-PCR provide important prognostic information in AML

Nucleophosmin (NPM1)-mutated acute myeloid leukemia (AML), which is recognized as a provisional entity in the World Health Organization 2008 classification of myeloid neoplasms, accounts for 30% of AML. We analyzed 1227 diagnostic and follow-up samples in 252 NPM1-mutated AML patients with 17 different NPM1 mutation-specific real-time quantitative polymerase chain reaction (RQ-PCR) assays. Paired diagnostic/relapse samples of 84 patients revealed stable NPM1 mutations in all cases, suggesting that they are pathogenetically early events and thus applicable for minimal residual disease detection. A total of 47 relapses were predictable because of an NPM1 mutation level (%NPM1/ABL1) increase of at least 1 log or in 15 cases because of NPM1 mutation levels not decreasing less than 3 log ranges. A high prognostic value of NPM1 levels was shown for 4 different intervals after therapy was initiated. Furthermore, thresholds of 0.1 and 0.01%NPM1/ABL1 during/after treatment discriminated between prognostic subgroups. Univariate analyses, including age, white blood cell count, blast count, CD34 positivity, FLT3 mutations status, FAB type, karyotype, NPM1 mutation type, and pretreatment NPM1 mutational level, showed that, besides NPM1 mutation level, only age and FLT3-LM mutation status were prognostically significant for EFS. Multivariate analysis, including age, FLT3-LM status, and NPM1 mutation level at different time points, demonstrated that NPM1 level was the most relevant prognostic factor during first-line treatment. Similar results were obtained in patients undergoing second-line chemotherapy or allogeneic stem cell transplantation.

A >or=1 log rise in RQ-PCR transcript levels defines molecular relapse in core binding factor acute myeloid leukemia and predicts subsequent morphologic relapse

Core binding factor acute myeloid leukemia (CBF AML), with t(8;21)(q22;q22), inv(16)(p13q22) or t(16;16)(p13;q22) and the associated fusion gene transcripts AML1/ETO or CBFbeta/MYH11, has a favourable clinical prognosis although significant numbers of patients still suffer relapse. We examined the prognostic utility of serial bone marrow minimal residual disease (MRD) monitoring by RQ-PCR in a cohort of patients with CBF AML with long term clinical follow-up. Twenty-nine patients were evaluated with a median follow of 34 months. Twelve relapses occurred at a median of 11 months (range 4 - 17) from diagnosis. RQ-PCR levels at diagnosis, post-induction chemotherapy and post-consolidation were not predictive of outcome. However, a >or=1 log(10) rise at any stage in transcript level relative to the level from a remission bone marrow sample correlated with inferior leukemia free survival (LFS) and imminent morphologic relapse (hazard ratio 8.6). Relapses occurred a median of 60 days (range 45 - 272) after a log(10) rise. A >or=1 log(10) rise in transcript levels strongly predicts subsequent morphologic relapse in CBF AML and therefore defines molecular relapse. Our data support a simple RQ-PCR model for prediction of impending relapse which has the potential for widespread clinical applicability. Prospective identification of high risk patients will enable clinical trials to assess the efficacy of treatment initiated at molecular relapse.

Acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous group of leukemias that result from clonal transformation of hematopoietic precursors through the acquisition of chromosomal rearrangements and multiple gene mutations. As a result of highly collaborative clinical research by pediatric cooperative cancer groups worldwide, disease-free survival has improved significantly during the past 3 decades. Further improvements in outcomes of children who have AML probably will reflect continued progress in understanding the biology of AML and the concomitant development of new molecularly targeted agents for use in combination with conventional chemotherapy drugs.

Feasibility of using the combined MDS-EVI1/EVI1 gene expression as an alternative molecular marker in acute myeloid leukemia: a report of four cases

To establish an additional marker for polymerase chain reaction (PCR)-based measurement of minimal residual disease (MRD) detection in acute myeloid leukemia (AML), the expression level of the combined MDS1-EVI1 and EVI1 gene was quantified by real-time reverse transcription PCR (RT-PCR) in four AML cases at initial presentation and as a follow-up marker during anti-leukemic therapy. Quantification of the MDS1-EVI1/EVI1 gene expression correlated closely to the clinical course of the disease in all four cases. A hematologic complete remission was accompanied by a reduction of MDS1-EVI1/ EVI1 expression levels of at least 2 log while persistent leukemia was reflected by an MDS1-EVI1/ EVI1 expression in the range of the primary diagnostic sample. After achieving a complete cytomorphologic remission, three patients relapsed after 154, 210, and 280 days, respectively. Molecular relapse was detected on the basis of increasing expression levels of MDS1-EVI/EVI 29, 36, and 93 days before hematologic manifestation. In conclusion, the combined MDS-EVI1/EVI1 gene may serve as an alternative MRD marker in AML, especially in samples where other specific markers are lacking.

Molecular Methods Used for Detection of Minimal Residual Disease Following Hematopoietic Stem Cell Transplantation in Myeloid Disorders

Monitoring of minimal residual disease (MRD) in patients with acute or chronic myeloid disorders is routinely performed after allogeneic or autologous transplantation. The detection of MRD helps to identify patients who are at high risk for leukemic relapse after transplantation. The most commonly used techniques for MRD detection are qualitative and quantitative PCR methods, fluorescence in situ hybridization (FISH), fluorescence-activated cell sorting (FACS), and cytogenetic analysis, which are often performed complementary in order to assess more precisely MRD. Here, we describe the most used sensitive real-time reverse-transcription (RT)-PCR methods for chronic and acute myeloid disorders. Besides protocols for real-time RT-PCR and multiplex RT-PCR procedures for the most common fusion-gene transcripts in acute and chronic myeloid disorders, methods for detection of disease-specific genetic mutated alterations as FLT3 gene-length mutations, and aberrantly expressed genes as WT1 gene transcripts, are described in detail for daily use.

Prognostic value of minimal residual disease (MRD) in acute myeloid leukemia (AML) with favorable cytogenetics [t(8;21) and inv(16)]

Most patients with acute myeloid leukemia (AML) and t(8;21) or inv(16) have a good prognosis with current anthracycline- and cytarabine-based protocols. Tandem analysis with flow cytometry (FC) and real-time RT-PCR (RQ-PCR) was applied to 55 patients, 28 harboring a t(8;21) and 27 an inv(16), including one case with a novel CBFbeta/MYH11 transcript. A total of 31% (n=17) of CR patients relapsed: seven with t(8;21) and 10 with inv(16). The mean amount of minimal residual disease (MRD) detected by FC in relapsed and nonrelapsed patients was markedly different: 0.3 vs 0.08% (P=0.002) at the end of treatment. The mean number of fusion transcript copies/ ABL x 10(4) also differed between relapsed and non-relapsed patients: 2385 vs 122 (P=0.001) after induction, 56 vs 7.6 after intensification (P=0.0001) and 75 vs 3.3 (P=0.0001) at the end of chemotherapy. Relapses were more common in patients with FC MRD level >0.1% at the end of treatment than in patients with < or = 0.1%: cumulative incidence of relapse (CIR) was 67 and 21% (P=0.03), respectively. Likewise, using RQ-PCR, a cutoff level of >10 copies at the end of treatment correlated with a high risk of relapse: CIR was 75% for patients with RQ-PCR >10 compared to 21% for patients with RQ-PCR levels < or = 10 (P=0.04). Combined use of FC and RQ-PCR may improve MRD detection, and provide useful clinical information on relapse kinetics in AML patients.

Real-time RT-PCR quantification of PRAME gene expression for monitoring minimal residual disease in acute myeloblastic leukaemia

BACKGROUND

Specific gene rearrangements are used for minimal residual disease (MRD) assessment, but are frequently lacking in leukaemias. In these cases, the quantification of PRAME (preferentially expressed antigen of melanoma) transcripts could be useful.

METHODS

PRAME transcripts were quantified by real-time RT-PCR in normal and leukaemic samples, and the results were compared with those of conventional RT-PCR. Basal expression of PRAME was determined in 25 blood samples and 25 bone marrow samples from healthy donors, as well as in 12 haematological cell lines (Jurkat, K562, HL60, DOHH2, IM9, Daudi, CEM, KG1, DG75, 8226, U937, Raji).

RESULTS

In paediatric acute myeloid leukaemia (AML) (n=22) and acute lymphoblastic leukaemia (ALL) (n=17), and in adult AML (n=20), abnormal PRAME expression was found in 41%, 35% and 40% of cases, respectively. To assess the sensitivity of PRAME for monitoring MRD, PRAME-positive t(8;21) AML samples with detectable AML1/ETO expression by conventional RT-PCR (n=17) were assessed for quantitative expression of AML1/ETO and PRAME. The expression of these genes was closely correlated. To confirm that PRAME expression was correlated with clinical data, the expression of PRAME was also sequentially followed in patients (n=13) from onset to cytological remission or relapse. The cytological and molecular data were highly correlated in all patients.

CONCLUSIONS

Our data confirm that PRAME quantification by real-time RT-PCR appears suitable for monitoring MRD in PRAME-positive leukaemia.

Quantitative assessment of minimal residual disease in acute myeloid leukemia carrying nucleophosmin (NPM1) gene mutations

Mutations in exon 12 of the nucleophosmin (NPM1) gene occur in about 60% of adult AML with normal karyotype. By exploiting a specific feature of NPM1 mutants, that is insertion at residue 956 or deletion/insertion at residue 960, we developed highly sensitive, real-time quantitative (RQ) polymerase chain reaction (PCR) assays, either in DNA or RNA, that are specific for various NPM1 mutations. In all 13 AML patients carrying NPM1 mutations at diagnosis, cDNA RQ-PCR showed >30 000 copies of NPM1-mutated transcript. A small or no decrease in copies was observed in three patients showing partial or no response to induction therapy. The number of NPM1-mutated copies was markedly reduced in 10 patients achieving complete hematological remission (five cases: <100 copies; five cases: 580-5046 copies). In four patients studied at different time intervals, the number of NPM1 copies closely correlated with clinical status and predicted impending hematological relapse in two. Thus, reliable, sensitive RQ-PCR assays for NPM1 mutations can now monitor and quantify MRD in AML patients with normal karyotype and NPM1 gene mutations.

Advances in real-time PCR: application to clinical laboratory diagnostics

The polymerase chain reaction (PCR) has become one of the most important tools in molecular diagnostics, providing exquisite sensitivity and specificity for detection of nucleic acid targets. Real-time monitoring of PCR has simplified and accelerated PCR laboratory procedures and has increased information obtained from specimens including routine quantification and differentiation of amplification products. Clinical diagnostic applications and uses of real-time PCR are growing exponentially, real-time PCR is rapidly replacing traditional PCR, and new diagnostic uses likely will emerge. This review analyzes the scope of present and potential future clinical diagnostic applications of this powerful technique. Critical discussions focus on basic concepts, variations, data analysis, instrument platforms, signal detection formats, sample collection, assay design, and execution of real-time PCR.

Monitoring of minimal residual disease in acute myeloid leukemia

Monitoring minimal residual disease (MRD) becomes increasingly important in the risk-adapted management of patients with acute myeloid leukemia (AML). The two most sensitive and quantitative methods for MRD detection are multiparameter flow cytometry (MFC) and real-time polymerase chain reaction (QRT-PCR). Fusion gene-specific PCR in AML is based on the RNA level, and thus in contrast to MFC expression levels rather than cell counts are assessed. For both methods independent prognostic values have been shown. The strong power of MFC has been shown mainly in the assessment of early clearance of the malignant clone. MRD levels in AML with fusion genes have the strongest prognostic power after the end of consolidation therapy. In addition, with QRT-PCR highly predictive initial expression levels can be assessed. With both methods early detection of relapse is possible. So far, validated PCR-based MRD was done with fusion genes that are detectable in only 20-25% of all AML MFC is superior since it is applicable for most AML. However, QRT-PCR is still more sensitive in most cases. Thus, it is desirable to establish new molecular markers for PCR-based studies. Large clinical trials will determine the role and place of immunologic and PCR-based monitoring in the prognostic stratification of patients with AML.

Biology and management of relapsed acute myeloid leukaemia

Disease relapse remains the major cause of treatment failure in adults with acute myeloid leukaemia (AML). This reflects both the failure of current salvage regimens and the absence of effective strategies to secure long-term disease-free survival in those patients who achieve a second remission. Recent progress in understanding the pathogenesis of relapsed disease has enabled the identification of a variety of dysregulated molecular pathways and these now provide a rational basis for the design of novel targeted therapies. At the same time, advances in allogeneic stem-cell transplantation have permitted the extension of the curative potential of allografting to patients in whom it was previously contraindicated. As a result, a range of novel drug and transplant therapies has become available in patients with relapsed AML, and it is realistic to anticipate that a co-ordinated assessment of their clinical and biological impact will provide the basis for the design of future, more effective treatments in relapsed disease.

Detection and monitoring of minimal residual disease by quantitative real-time PCR

BACKGROUND

The detection of malignant cells by quantitative real-time PCR has become state of the art for diagnosis, monitoring response to treatment and detection of minimal residual disease (MRD) in patients with leukemia or lymphoma. In order to be used in high-throughput analyses technical details have to be standardized to improve reproducibility and comparability of quantitative results obtained in different laboratories.

METHODS

Molecular monitoring of disease activity during and after treatment based on the detection of malignant cells in circulation or bone marrow by quantitative real-time PCR will be helpful to develop individualized treatment strategies for every patient.

CONCLUSIONS

The effectiveness of any kind of innovative treatment with specific antibodies, cellular immunotherapy or molecules designed for specific targets of tumor cells can be controlled at a very high level of sensitivity and accuracy. Based on quantitative results indicative for success or treatment failure, therapeutic changes upon the detection of progressive disease at the molecular level can be made even before symptoms or signs of clinical relapse occur. Hopefully, this will lead to higher cure rates and improved long-term survival.

Molecular genetic analysis of haematological malignancies: I. Acute leukaemias and myeloproliferative disorders

Molecular genetic techniques are now routinely applied to haematological malignancies within a clinical laboratory setting. The detection of genetic rearrangements not only assists with diagnosis and treatment decisions, but also adds important prognostic information. In addition, genetic rearrangements associated with leukaemia can be used as molecular markers allowing the detection of low levels of residual disease. This review will concentrate on the application of molecular genetic techniques to the acute leukaemias and myeloprolferative disorders.

Prognostic impact of RT-PCR-based quantification of WT1 gene expression during MRD monitoring of acute myeloid leukemia

In search for general PCR targets for minimal residual disease (MRD) studies in acute myeloid leukemia (AML), Wilms' tumor gene 1 (WT1) expression was assessed by real-time RT-PCR relative to the control gene ABL in 569 archived samples of AML patients (pts). Pts were analyzed at diagnosis (n=116) and during follow-up (n=105, median 4 times, range 2--17). Median follow-up time was 258 days (range 16--1578 days). In 66 pts, the WT1 expression was analyzed in comparison to a second PCR marker or to multiparameter flow cytometry. Quantitative WT1 levels correlated to the clinical course or a second marker in 83-96% of the cases. Prognostic significance of WT1 levels was analyzed at diagnosis and three intervals: (1) days 16--60, (2) days 61--120, and (3) days 121--180 after start of chemotherapy. Higher levels of WT1 expression were associated with shorter overall survival (OS) and event-free survival (EFS) within intervals 2 and 3 but not at diagnosis or interval 1. In addition, within these intervals, WT1/ABL levels <or=0.4% were associated with improved OS and EFS. An increase of WT1 levels was detected in 16/44 cases, which subsequently relapsed within a median of 38 days (range 8--180 days). In conclusion, quantification of WT1 may be used for MRD studies and for prognostification in AML.