Residual Disease Monitoring in Childhood Acute Myeloid Leukemia by Multiparameter Flow Cytometry: The MRD-AML-BFM Study Group

Prognostic significance of multiparametric flow cytometry minimal residual disease at two time points after induction in pediatric acute myeloid leukemia

BACKGROUND

Prompt response to induction chemotherapy is a prognostic factor in pediatric acute myeloid leukemia. In this study, we aimed to evaluate the prognostic significance of multiparametric flow cytometry-minimal residual disease (MFC-MRD), assessed at the end of the first and second induction courses.

METHODS

MFC-MRD was performed at the end of the first induction (TP1) in 524 patients and second induction (TP2) in 467 patients who were treated according to the modified Medical Research Council (UK) acute myeloid leukemia 15 protocol.

RESULTS

Using a 0.1% cutoff level, patients with MFC-MRD at the two time points had lower event-free survival and overall survival. Only the TP2 MFC-MRD level could predict the outcome in a separate analysis of high and intermediate risks based on European LeukemiaNet risk stratification and KMT2A rearrangement. The TP2 MFC-MRD level could further differentiate the prognosis of patients into complete remission or non-complete remission based on morphological evaluation. Multivariate analysis indicated the TP2 MFC-MRD level as an independent adverse prognostic factor for event-free survival and overall survival. When comparing patients with MFC-MRD ≥ 0.1%, those who underwent hematopoietic stem cell transplant during the first complete remission had significantly higher 5-year event-free survival and overall survival and lower cumulative incidence of relapse than those who only received consolidation chemotherapy.

CONCLUSIONS

The TP2 MFC-MRD level can predict the outcomes in pediatric patients with acute myeloid leukemia and help stratify post-remission treatment.

Risk-Stratified Therapy for Pediatric Acute Myeloid Leukemia

Acute Myeloid Leukemia (AML) is the second most common type of leukemia in children. Recent advances in high-resolution genomic profiling techniques have uncovered the mutational landscape of pediatric AML as distinct from adult AML. Overall survival rates of children with AML have dramatically improved in the past 40 years, currently reaching 70% to 80% in developed countries. This was accomplished by the intensification of conventional chemotherapy, improvement in risk stratification using leukemia-specific cytogenetics/molecular genetics and measurable residual disease, appropriate use of allogeneic hematopoietic stem cell transplantation, and improvement in supportive care. However, the principle therapeutic approach for pediatric AML has not changed substantially for decades and improvement in event-free survival is rather modest. Further refinements in risk stratification and the introduction of emerging novel therapies to contemporary therapy, through international collaboration, would be key solutions for further improvements in outcomes.

Measurable residual disease study through three different methods can anticipate relapse and guide pre-emptive therapy in childhood acute myeloid leukemia

PURPOSE

Although outcomes of children with acute myeloid leukemia (AML) have improved over the last decades, around one-third of patients relapse. Measurable (or minimal) residual disease (MRD) monitoring may guide therapy adjustments or pre-emptive treatments before overt hematological relapse.

METHODS

In this study, we review 297 bone marrow samples from 20 real-life pediatric AML patients using three MRD monitoring methods: multiparametric flow cytometry (MFC), fluorescent in situ hybridization (FISH) and polymerase chain reaction (PCR).

RESULTS

Patients showed a 3-year overall survival of 73% and a 3-year event-free survival of 68%. Global relapse rate was of 25%. All relapses were preceded by the reappearance of MRD detection by: (1) MFC (p = 0.001), (2) PCR and/or FISH in patients with an identifiable chromosomal translocation (p = 0.03) and/or (3) one log increase of Wilms tumor gene 1 (WT1) expression in two consecutive samples (p = 0.02). The median times from MRD detection to relapse were 26, 111, and 140 days for MFC, specific PCR and FISH, and a one log increment of WT1, respectively.

CONCLUSIONS

MFC, FISH and PCR are complementary methods that can anticipate relapse of childhood AML by weeks to several months. However, in our series, pre-emptive therapies were not able to prevent disease progression. Therefore, more sensitive MRD monitoring methods that further anticipate relapse and more effective pre-emptive therapies are needed.

MRD Monitoring by Multiparametric Flow Cytometry in AML: Is It Time to Incorporate Immune Parameters?

Simple Summary

Measurable residual disease (MRD) is emerging as an important prognostic and predictive biomarker in acute myeloid leukemia (AML). However, its use is currently hampered by the disparity and lack of harmonization between the available MRD methodologies. In addition, the current assessment of MRD in AML focuses only on the quantification of the residual leukemic burden, without addressing the parallel alterations of the antineoplastic immune response that can critically affect the course and outcome of AML, often despite MRD persistence. Incorporating parameters of immune competence provides more consistency with the biological concept of MRD and may lead to higher accuracy. Multiparameter flow cytometry (MFC) is a highly efficacious and sensitive technology for the thorough and synchronous investigation of the kinetics of both antitumor immunity and the leukemic clone. MFC-based MRD provides the platform for the development of a composite leukemia- and immune-based biomarker which can outcompete the current MRD assessment.

Abstract

Acute myeloid leukemia (AML) is a heterogeneous group of clonal myeloid disorders characterized by intrinsic molecular variability. Pretreatment cytogenetic and mutational profiles only partially inform prognosis in AML, whereas relapse is driven by residual leukemic clones and mere morphological evaluation is insensitive for relapse prediction. Measurable residual disease (MRD), an independent post-diagnostic prognosticator, has recently been introduced by the European Leukemia Net as a new outcome definition. However, MRD techniques are not yet standardized, thus precluding its use as a surrogate endpoint for survival in clinical trials and MRD-guided strategies in real-life clinical practice. AML resistance and relapse involve a complex interplay between clonal and immune cells, which facilitates the evasion of the leukemic clone and which is not taken into account when merely quantifying the residual leukemia. Multiparameter flow cytometry (MFC) offers the possibility of capturing an overall picture of the above interactions at the single cell level and can simultaneously assess the competence of anticancer immune response and the levels of residual clonal cells. In this review, we focus on the current status of MFC-based MRD in diverse AML treatment settings and introduce a novel perspective of combined immune and leukemia cell profiling for MRD assessment in AML.

Allogeneic hematopoietic stem cell transplantation for pediatric acute myeloid leukemia in first complete remission: a meta-analysis

Identification of pediatric patients with acute myeloid leukemia (AML) candidates to receive allogeneic hematopoietic stem cell transplantation (allo-HSCT) in first complete remission (CR1) is still a matter of debate. Currently, transplantation is reserved to patients considered at high risk of relapse based on cytogenetics, molecular biology, and minimal residual disease (MRD) assessment. However, no randomized clinical trial exists in the literature comparing transplantation with other types of consolidation therapy. Here, we provide an up-to-date meta-analysis of studies comparing allo-HSCT in CR1 with chemotherapy alone as a post-remission treatment in high-risk pediatric AML. The literature search strategy identified 10 cohorts from 9 studies performing as-treated analysis. The quantitative synthesis showed improved overall survival (OS) (relative risk, 1.15; 95% confidence interval [CI], 1.06-1.24; P = 0.0006) and disease-free survival (relative risk, 1.31; 95% CI, 1.17-1.47; P = 0.0001) in the allo-HSCT group, with increased relapse rate in the chemotherapy group (relative risk, 1.26; 95% CI, 1.07-1.49; P = 0.006). Sensitivity analysis including prospective studies alone and excluding studies that reported the comparison only on intermediate-risk patients confirmed the benefit of allo-HSCT on OS. Further research should focus on individualizing allo-HSCT indications based on molecular stratification and MRD monitoring.

Measurable residual disease (MRD) status before allogeneic hematopoietic cell transplantation impact on secondary acute myeloid leukemia outcome. A Study from the Acute Leukemia Working Party (ALWP) of the European society for Blood and Marrow Transplantation (EBMT)

Measurable residual disease (MRD) assessment before allogeneic hematopoietic cell transplantation (HCT) may help physicians to identify a subgroup of patients at high risk of relapse for de novo acute myeloid leukemia (AML) but its relevance among patients affected by secondary AML (sAML) is still unknown. We assessed the impact of MRD among 318 adult patients with sAML who received an allogeneic HCT in first complete remission. At the time of HCT, a total of 208 (65%) patients achieved MRD negativity, while 110 (35%) had positive MRD. 2-year overall survival (OS) was 58.8 % (95% CI 52.2-64.9) with leukemia-free survival (LFS) of 50.0 % (95% CI 43.7-56.1), relapse incidence of 34.2% (95% CI 28.4-40.1) and non-relapse mortality (NRM) of 23.3 % (95% CI 19-27.7) for the entire cohort. In multivariate analysis, HCT recipients with KPS ≥ 90 experienced less disease recurrence (HR 0.61, 95% CI 0.4-0.94) with better LFS (HR 0.63, 95% CI 0.44-0.89) and OS (HR 0.58, 95% CI 0.39-0.86). There were no differences in major clinical endpoints between patients with MRD-positive and MRD-negative status at the time of HCT. Pre-transplantation assessment of MRD was not informative on post-HCT outcomes in this retrospective registry-based analysis among patients affected by sAML.

Measurable Residual Disease in High-Risk Acute Myeloid Leukemia

Simple Summary

Assessment of measurable residual disease (MRD) identifies small numbers of acute myeloid leukemia (AML) cells that may remain after initiating treatment. The achievement of MRD negativity (no detectable AML cells remaining) typically predicts better outcomes for patients with AML. Some patients with AML have disease characteristics that put them at a higher risk of treatment failure or relapse; while outcomes for patients with high-risk AML are historically poor with traditional chemotherapy regimens, newer chemotherapy formulations (i.e., CPX-351) and targeted therapies may be more effective in achieving MRD negativity in these patients. Currently, there is no agreement on the best method for determining whether a patient has achieved MRD negativity, and the use of several different methods makes it difficult to compare outcomes across studies. Despite these challenges, regular monitoring of patients for the achievement of MRD negativity will become increasingly important in the routine management of patients with high-risk AML.

Abstract

Mounting evidence suggests measurable residual disease (MRD) assessments are prognostic in acute myeloid leukemia (AML). High-risk AML encompasses a subset of AML with poor response to therapy and prognosis, with features such as therapy-related AML, an antecedent hematologic disorder, extramedullary disease (in adults), and selected mutations and cytogenetic abnormalities. Historically, few patients with high-risk AML achieved deep and durable remission with conventional chemotherapy; however, newer agents might be more effective in achieving MRD-negative remission. CPX-351 (dual-drug liposomal encapsulation of daunorubicin/cytarabine at a synergistic ratio) demonstrated MRD-negativity rates of 36–64% across retrospective studies in adults with newly diagnosed high-risk AML and 84% in pediatric patients with first-relapse AML. Venetoclax (BCL2 inhibitor) demonstrated MRD-negativity rates of 33–53% in combination with hypomethylating agents for high-risk subgroups in studies of older adults with newly diagnosed AML who were ineligible for intensive therapy and 65% in combination with chemotherapy in pediatric patients with relapsed/refractory AML. However, there is no consensus on optimal MRD methodology in AML, and the use of different techniques, sample sources, sensitivity thresholds, and the timing of assessments limit comparisons across studies. Robust MRD analyses are needed in future clinical studies, and MRD monitoring should become a routine aspect of AML management.

Pediatric Acute Myeloid Leukemia—Past, Present, and Future

This review reports about the main steps of development in pediatric acute myeloid leukemia (AML) concerning diagnostics, treatment, risk groups, and outcomes. Finally, a short overview of present and future approaches is given.

A novel event-free survival endpoint in locally advanced pancreatic cancer

The treatment paradigm for locally advanced pancreatic cancer (LAPC) is evolving rapidly. The development of neoadjuvant therapies composed of combination therapies and the evaluation of their impact on conversion to borderline resectable (BR) status, resection, and ultimately overall survival (OS) are presently being pursued. These efforts justify re-visiting study endpoints in order to better predict therapeutic effects on OS, by capturing not only the achievement of R0 resection at the end of induction therapy but also the long-term reductions in the rate of local and distal recurrence. The proposed herein event-free survival (EFS) endpoint, with its novel definition specific to LAPC, is formulated to achieve these objectives. It is an analog to disease-free survival (DFS) endpoint in the adjuvant setting applied to the neoadjuvant setting and may be a valuable surrogate endpoint for this patient population.

Recent Advances in the Management of Pediatric Acute Myeloid Leukemia-Report of the Hungarian Pediatric Oncology-Hematology Group

Simple Summary

The outcome of pediatric AML improved considerably worldwide during the past few decades. Hereby, we summarize the therapeutic results of pediatric AML patients registered between 2012 and 2019 in Hungary. As compared to our previous results, improvement was registered in event-free (EFS) and overall (OS) survival, which can be attributed to the application of contemporary diagnostic and therapeutic guidelines, advanced supportation, and higher efficacy of hematopoietic stem cell transplantation. Between 2016 and 2019, a statistically significant increment of 2-year EFS was confirmed over the period between 2012 and 2015. The most prominent progress was observed in acute promyelocytic leukemia (APL). Multidimensional flow cytometry made possible the prompt introduction of ATRA in two cases with M3v, who also represent the first pediatric APL patients in Hungary to be treated with arsenic-trioxide. Besides joining multinational pediatric AML treatment groups, our future aims include the introduction of centralized treatment centers and diagnostic facilities.

Abstract

Outcome measures of pediatric acute myeloid leukemia (AML) improved considerably between 1990 and 2011 in Hungary. Since 2012, efforts of the Hungarian Pediatric Oncology-Hematology Group (HPOG) included the reduction in the number of treatment centers, contemporary diagnostic procedures, vigorous supportation, enhanced access to hematopoietic stem cell transplantation (HSCT), and to targeted therapies. The major aim of our study was to evaluate AML treatment results of HPOG between 2012 and 2019 with 92 new patients registered (52 males, 40 females, mean age 7.28 years). Two periods were distinguished: 2012–2015 and 2016–2019 (55 and 37 patients, respectively). During these periods, 2 y OS increased from 63.6% to 71.4% (p = 0.057), and the 2 y EFS increased significantly from 56.4% to 68.9% (p = 0.02). HSCT was performed in 37 patients (5 patients received a second HSCT). We demonstrate advances in the diagnosis and treatment of acute promyelocytic leukemia (APL) in two cases. Early diagnosis and follow-up were achieved by multidimensional flow cytometry and advanced molecular methods. Both patients were successfully treated with all-trans retinoic acid and arsenic-trioxide, in addition to chemotherapy. In order to meet international standards of pediatric AML management, HPOG will further centralize treatment centers and diagnostic facilities and join efforts with international study groups.

Impact of measurable residual disease by decentralized flow cytometry: a PETHEMA real-world study in 1076 patients with acute myeloid leukemia

The role of decentralized assessment of measurable residual disease (MRD) for risk stratification in acute myeloid leukemia (AML) remains largely unknown, and so it does which methodological aspects are critical to empower the evaluation of MRD with prognostic significance, particularly if using multiparameter flow cytometry (MFC). We analyzed 1076 AML patients in first remission after induction chemotherapy, in whom MRD was evaluated by MFC in local laboratories of 60 Hospitals participating in the PETHEMA registry. We also conducted a survey on technical aspects of MRD testing to determine the impact of methodological heterogeneity in the prognostic value of MFC. Our results confirmed the recommended cutoff of 0.1% to discriminate patients with significantly different cumulative-incidence of relapse (-CIR- HR:0.71, P < 0.001) and overall survival (HR: 0.73, P = 0.001), but uncovered the limited prognostic value of MFC based MRD in multivariate and recursive partitioning models including other clinical, genetic and treatment related factors. Virtually all aspects related with methodological, interpretation, and reporting of MFC based MRD testing impacted in its ability to discriminate patients with different CIR. Thus, this study demonstrated that "real-world" assessment of MRD using MFC is prognostic in patients at first remission, and urges greater standardization for improved risk-stratification toward clinical decisions in AML.

Role of Minimal Residual Disease Testing in Acute Myeloid Leukemia

Minimal or measurable residual disease (MRD) after therapy is the most important independent prognostic factor in acute myeloid leukemia. MRD measured by multiparametric flow cytometry and real-time quantitative polymerase chain reaction has been integrated into risk stratification and used to guide future treatment strategies. Recent technological advances have allowed the application of the novel molecular method, high-throughput sequencing, in MRD detection in clinical practice to improve sensitivity and specificity. Randomized studies are needed to address outstanding issues, including the optimal methods and timing of MRD testing and interlaboratory standardization to facilitate comparisons, to further improve MRD-directed interventions.

Treatment of acute myeloid leukemia in children: A practical perspective

Pediatric acute myeloid leukemia (AML) is a heterogeneous disease that requires a multifaceted treatment approach. Although outcomes for low-risk AML have improved significantly over recent decades, high-risk AML continues to be associated with an adverse prognosis. Recent advances in molecular diagnostics, risk stratification, and supportive care have contributed to improvements in outcomes in pediatric AML. Targeted approaches, for example, the use of tyrosine kinase inhibitors to treat FLT3-ITD AML, offer promise and are currently undergoing clinical investigation in pediatric patients. New approaches to hematopoietic stem cell transplantation, including the use of haploidentical donors, are significantly expanding donor options for patients with high-risk AML. This review provides an overview of recent advances in the treatment of pediatric AML that are likely to have clinical impact and reshape the standard of care.

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.

Morphologic remission status is limited compared to ΔN flow cytometry: a Children's Oncology Group AAML0531 report

Risk stratification for acute myeloid leukemia (AML) uses molecular and cytogenetic abnormalities identified at diagnosis. Response to therapy informs risk, and morphology continues to be used more frequently than flow cytometry. Herein, the largest cohort of pediatric patients prospectively assessed for measurable residual disease (MRD) by flow cytometry (N = 784) is reported. The "difference from normal" (ΔN) technique was applied: 31% of all patients tested positive (AML range, 0.02% to 91%) after the first course of treatment on Children's Oncology Group study AAML0531. Detection of MRD following initial chemotherapy proved the strongest predicator of overall survival (OS) in univariable and multivariable analyses, and was predictive of relapse risk, disease-free survival, and treatment-related mortality. Clearance of MRD after a second round of chemotherapy did not improve survival. The morphologic definition of persistent disease (>15% AML) failed 27% of the time; those identified as MRD- had superior outcomes. Similarly, for patients not achieving morphologic remission (>5% blasts), 36% of patients were MRD- and had favorable outcomes compared with those who were MRD+ (P < .001); hence an increase in myeloid progenitor cells can be favorable when ΔN classifies them as phenotypically normal. Furthermore, ΔN reclassified 20% of patients in morphologic remission as having detectable MRD with comparable poor outcomes. Retrospective analysis using the relapse phenotype as a template demonstrated that 96% of MRD- patients had <0.02% of the relapse immunophenotype in their end of induction 1 marrow. Thus, the detection of abnormal myeloid progenitor cells by ΔN is both specific and sensitive, with a high predictive signal identifiable early in treatment. This trial was registered at www.clinicaltrials.gov as #NCT00372593.

Predictive impact of residual disease detected using multiparametric flow cytometry on risk stratification of paediatric acute myeloid leukaemia with normal karyotype

INTRODUCTION

Residual disease (RD) detected using multiparametric flow cytometry (MFC) is an independent predictive variable of relapse in acute myeloid leukaemia (AML). However, RD thresholds and optimal assessment time points remain to be validated.

MATERIAL AND METHODS

We investigated the significance of RD after induction therapy in paediatric AML with normal karyotype between June 2008 and June 2018. Bone marrow samples from 73 patients were collected at the end of the first (BMA-1) and second (BMA-2) induction courses to monitor RD using MFC.

RESULTS

Presence of RD after BMA-1 and/or BMA-2 correlated with poor relapse-free (RFS) and overall survival at 0.1% RD cutoff level. Receiver operating characteristic curve showed that RD cutoff levels of 1.3% and 0.5% after BMA-1 and BMA-2, respectively, predicted events with the highest sensitivity and specificity. In multivariable analysis, RD after BMA-2 was the strongest independent risk predictor for poor RFS (hazard ratio 2.934; 95% confidence interval: 1.106-7.782; P = .031).

CONCLUSIONS

Our study therefore suggests that an RD level ≥0.5% after BMA-2 has a significant predictive impact on the prognosis of AML patients having normal karyotype and thus guide the stratification of treatment strategies.

Measurable residual disease status and outcome of transplant in acute myeloid leukemia in second complete remission: a study by the acute leukemia working party of the EBMT

Measurable residual disease (MRD) prior to hematopoietic cell transplant (HCT) for acute myeloid leukemia (AML) in first complete morphological remission (CR1) is an independent predictor of outcome, but few studies address CR2. This analysis by the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation registry assessed HCT outcomes by declared MRD status in a cohort of 1042 adult patients with AML CR2 at HCT. Patients were transplanted 2006–2016 from human leukocyte antigen (HLA) matched siblings (n = 719) or HLA 10/10 matched unrelated donors (n = 293). Conditioning was myeloablative (n = 610) or reduced-intensity (n = 432) and 566 patients (54%) had in-vivo T cell depletion. At HCT, 749 patients (72%) were MRD negative (MRD NEG) and 293 (28%) were MRD positive (MRD POS). Time from diagnosis to HCT was longer in MRD NEG than MRD POS patients (18 vs. 16 months (P < 0.001). Two-year relapse rates were 24% (95% CI, 21–28) and 40% (95% CI, 34–46) in MRD NEG and MRD POS groups (P < 0.001), respectively. Leukemia-free survival (LFS) was 57% (53–61) and 46% (40–52%), respectively (P = 0.001), but there was no difference in terms of overall survival. Prognostic factors for relapse and LFS were MRD NEG status, good risk cytogenetics, and longer time from diagnosis to HCT. In-vivo T cell depletion predicted relapse.

Aberrant myelomonocytic CD56 expression in Down syndrome is frequent and not associated with leukemogenesis

Children with Down syndrome (DS) are at an increased risk of developing transient abnormal myelopoiesis (TAM) and acute leukemia. Aberrant expression of CD56 has been observed on myeloid leukemic blasts in DS patients. In general, CD56 expression in acute myeloid leukemia (AML) is considered a promoter of leukemogenesis. We did a retrospective flow cytometric study to investigate mature myelomonocytic cell CD56 expression patterns in TAM, non-TAM, and leukemia cases with DS. Flow cytometric analysis showed that granulocyte and monocyte aberrant/dysplastic CD56 expression is an inherent characteristic of most DS patients irrespective of the presence of TAM or leukemia. Increased CD56 expression in monocyte and granulocyte populations in DS could be multifactorial; greater expression of RUNX1 secondary to the gene dose effect of trisomy 21 along with the maturational state of the cells are the potential contributors. Unlike AML seen in non-DS patients, CD56 overexpression in DS AML cases does not appear to play a role in leukemogenesis.

Measurable residual disease in pediatric acute myeloid leukemia: a systematic review

Introduction: A systematic review was performed to assess the prognostic value of Measurable Residual Disease (MRD) during treatment, for relapse and overall survival in pediatric acute myeloid leukemia (AML).Areas covered: A systematic search of available literature was performed to identify original full-text articles concerning MRD as prognostic for relapse and survival in pediatric AML. Thirteen studies were included, and in all studies, MRD positivity during treatment was associated with worse clinical outcome. MRD positivity was significantly associated with a higher probability of relapse in eleven studies. However, MRD negativity does not exclude the possibility of relapse in pediatric AML, while positivity early during therapy does not exclude cure.Expert opinion: MRD positivity during treatment has emerged as the most powerful prognostic factor in pediatric AML concerning relapse and overall survival and is useful for risk-group adapted treatment. Future studies should identify the optimal time-point(s) for MRD measurements and the optimal technique, to further improve its prognostic significance.

Association of Measurable Residual Disease With Survival Outcomes in Patients With Acute Myeloid Leukemia: A Systematic Review and Meta-analysis

IMPORTANCE

Measurable residual disease (MRD) refers to neoplastic cells that cannot be detected by standard cytomorphologic analysis. In patients with acute myeloid leukemia (AML), determining the association of MRD with survival may improve prognostication and inform selection of efficient clinical trial end points.

OBJECTIVE

To examine the association between MRD status and disease-free survival (DFS) and overall survival (OS) in patients with AML using scientific literature.

DATA SOURCES

Clinical studies on AML published between January 1, 2000, and October 1, 2018, were identified via searches of PubMed, Embase, and MEDLINE.

STUDY SELECTION

Literature search and study screening were performed according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. Studies that assessed DFS or OS by MRD status in patients with AML were included. Reviews, non-English-language articles, and studies reporting only outcomes after hematopoietic cell transplantation or those with insufficient description of MRD information were excluded.

DATA EXTRACTION AND SYNTHESIS

Study sample size, median patient age, median follow-up time, MRD detection method, MRD assessment time points, AML subtype, specimen source, and survival outcomes were extracted. Meta-analyses were performed separately for DFS and OS using bayesian hierarchical modeling.

MAIN OUTCOMES AND MEASURES

Meta-analyses of survival probabilities and hazard ratios (HRs) were conducted for OS and DFS according to MRD status.

RESULTS

Eighty-one publications reporting on 11 151 patients were included. The average HR for achieving MRD negativity was 0.36 (95% bayesian credible interval [CrI], 0.33-0.39) for OS and 0.37 (95% CrI, 0.34-0.40) for DFS. The estimated 5-year DFS was 64% for patients without MRD and 25% for those with MRD, and the estimated OS was 68% for patients without MRD and 34% for those with MRD. The association of MRD negativity with DFS and OS was significant for all subgroups, with the exception of MRD assessed by cytogenetics or fluorescent in situ hybridization.

CONCLUSIONS AND RELEVANCE

The findings of this meta-analysis suggest that achievement of MRD negativity is associated with superior DFS and OS in patients with AML. The value of MRD negativity appears to be consistent across age groups, AML subtypes, time of MRD assessment, specimen source, and MRD detection methods. These results support MRD status as an end point that may allow for accelerated evaluation of novel therapies in AML.

Utility of Immunophenotypic Measurable Residual Disease in Adult Acute Myeloid Leukemia-Real-World Context

Introduction: One of the mainstays of chemotherapy in acute myeloid leukemia (AML) is induction with a goal to achieve morphological complete remission (CR). However, not all patients by this remission criterion achieve long-term remission and a subset relapse. This relapse is explained by the presence of measurable residual disease (MRD).

Methods: We accrued 451 consecutive patients of adult AML (from March 2012 to December 2017) after informed consent. All patients received standard chemotherapy. MRD testing was done at post-induction and, if feasible, post-consolidation using 8- and later 10-color FCM. Analysis of MRD was done using a combination of difference from normal and leukemia-associated immunophenotype approaches. Conventional karyotyping and FISH were done as per standard recommendations, and patients were classified into favorable, intermediate, and poor cytogenetic risk groups. The presence of FLT3-ITD, NPM1, and CEBPA mutations was detected by a fragment length analysis-based assay.

Results: As compared to Western data, our cohort of patients was younger with a median age of 35 years. There were 62 induction deaths in this cohort (13.7%), and 77 patients (17.1%) were not in morphological remission. The median follow-up was 26.0 months. Poor-risk cytogenetics and the presence of FLT3-ITD were significantly associated with inferior outcome. The presence of post-induction MRD assessment was significantly associated with adverse outcome with respect to OS (p = 0.01) as well as RFS (p = 0.004). Among established genetic subgroups, detection of MRD in intermediate cytogenetic and NPM1 mutated groups was also highly predictive of inferior outcome. On multivariate analysis, immunophenotypic MRD at the end of induction and FLT3-ITD emerged as independent prognostic factors predictive for outcome.

Conclusion: This is the first data from a resource-constrained real-world setting demonstrating the utility of AML MRD as well as long-term outcome of AML. Our data is in agreement with other studies that determination of MRD is extremely important in predicting outcome. AML MRD is a very useful guide for guiding post-remission strategies in AML and should be incorporated into routine treatment algorithms.

Unrelated donor hematopoietic stem cell transplantation for pediatric de novo acute myeloid leukemia with intermediate- or high-risk cytogenetics

The role of unrelated donor HSCT for children with de novo AML in CR1 is controversial. We performed this study to investigate the feasibility of unrelated donor HSCT who initially had intermediate- or high-risk cytogenetics. We retrospectively reviewed medical records of patients with AML who received unrelated HSCT in CR1 at Samsung Medical Center between November 2001 and January 2012. Patients were allocated based on karyotype at diagnosis as follows: (a) low-risk: inv(16), t(16;16), t(8;21), and t(15;17); (b) high-risk: -5, 5q-, -7, 3q abnormalities, t(8;16), t(6;9), t(6;11), t(6;21), t(10;11), complex karyotype (≥3 abnormalities), and acute megakaryocytic leukemia without t(1;22); and (c) IR: all the other karyotypes including normal. Patients in intermediate- or high-risk group who were transplanted with either unrelated CB or matched unrelated BM/mobilized PB in their CR1 were included in this study. The projected OS and EFS rates were 74.9% and 71.1%, respectively, with a median follow-up of 87.3 months after transplantation. The EFS was 70.1%, 80.7%, and 73.9% for CB, BM, and mobilized PB groups, respectively (P = 0.89), and 73.9% and 70.6% for IR and high-risk groups (P = 0.76). The leading cause of death was relapse (n = 8), and only one patient died from non-relapse cause. Unrelated donor HSCT seems a feasible approach for children with intermediate- or high-risk AML in CR1. Relapse remains the leading cause of treatment failure among these patients.

Optimal Measurable Residual Disease Testing for Acute Myeloid Leukemia

Increasing evidence supports the prognostic significance of measurable residual disease (MRD) in acute myeloid leukemia (AML). Dynamic MRD assessment for patients with AML complements baseline patient risk assessment factors in determining patient prognosis. MRD status may also be helpful in informing therapeutic decisions. The European Leukemia Net MRD working party recently issued consensus recommendations for the use of MRD in AML. The Food and Drug Administration also issued advice for using MRD in trials of hematologic malignancies. This article discusses MRD testing, highlights the challenges in adopting MRD testing in clinical practice, and provides insights into the future of the field.

Identifying leukemia-associated immunophenotype-based individualized minimal residual disease in acute myeloid leukemia and its prognostic significance

Based on the leukemia-associated immunophenotypes (LAIPs), minimal residual disease (MRD) related to the outcome can be detected by multiparameter flow cytometry in acute myeloid leukemia (AML) patients. Although 0.1% was commonly used as a cutoff value, measurable MRD or MRD level below 0.1% has also been associated with prognostic significance and more sensitive thresholds (<0.1%) are required for improving AML prognosis prediction. In this study, 292 adult patients diagnosed with AML (non-M3) were enrolled, 36 kinds of LAIPs were identified, and the baseline expression levels in normal or regenerating bone marrows of each kind of LAIP were established, which ranged from <2.00 × 10^-5 to 5.71 × 10^-4 . The baseline level of each LAIP was considered as the individual threshold for MRD assessment. MRD statuses stratified by 0.1% and individual threshold were termed as 0.1%-MRD and individual-MRD, respectively. The patients of individual-MRD^neg showed significantly better survival compared with those of 0.1%-MRD^neg /individual-MRD^pos or 0.1%-MRD^pos . Multivariate analysis showed that when time points of complete remission, post the first and second consolidation courses, were considered, only individual-MRD post second consolidation presented independent prognostic value. Notably, in patients of cytogenetic/molecular low-risk (LR) or intermediate-risk (IR), the individual-MRD status could identify the patients with significantly different outcomes, while 0.1%-MRD status could not. Furthermore, among the patients of the LR or IR group which received chemotherapy only, those with individual-MRD^neg status presented favorable survival, which was comparable with that of the patients accepted allogeneic hematopoietic stem cell transplantation (ASCT). This approach is useful in the selection of an ASCT strategy for clinical practice.

Measurable residual disease testing for personalized treatment of acute myeloid leukemia

This review summarizes - with the practicing hematologist in mind - the methods used to determine measurable residual disease (MRD) in everyday practice with some future perspectives, and the current knowledge about the prognostic impact of MRD on outcome in acute myeloid leukemia (AML), excluding acute promyelocytic leukemia. Possible implications for choice of MRD method, timing of MRD monitoring, and guidance of therapy are discussed in general and in some detail for certain types of leukemia with specific molecular markers to monitor, including core binding factor (CBF)-leukemias and NPM1-mutated leukemias.

Flow-Cytometric Monitoring of Minimal Residual Disease in Pediatric Patients With Acute Myeloid Leukemia: Recent Advances and Future Strategies

Minimal residual disease (MRD) by multiparametric flow cytometry (MFC) has been recently shown as a strong and independent prognostic marker of relapse in pediatric AML (pedAML) when measured at specific time points during Induction and/or Consolidation therapy. Hence, MFC-MRD has the potential to refine the current strategies of pedAML risk stratification, traditionally based on the cytogenetic and molecular genetic aberrations at diagnosis. Consequently, it may guide the modulation of therapy intensity and clinical decision making. However, the use of non-standardized protocols, including different staining panels, analysis, and gating strategies, may hamper a broad implementation of MFC-MRD monitoring in clinical routine. Besides, the thresholds of MRD positivity still need to be validated in large, prospective and multi-center clinical studies, as well as optimal time points of MRD assessment during therapy, to better discriminate patients with different prognosis. In the present review, we summarize the most relevant findings on MFC-MRD testing in pedAML. We examine the clinical significance of MFC-MRD and the recent advances in its standardization, including innovative approaches with an automated analysis of MFC-MRD data. We also touch upon other technologies for MRD assessment in AML, such as quantitative genomic breakpoint PCR, current challenges and future strategies to enable full incorporation of MFC-MRD into clinical practice.

Loss of plasmacytoid dendritic cell differentiation is highly predictive for post-induction measurable residual disease and inferior outcomes in acute myeloid leukemia

Measurable residual disease is associated with inferior outcomes in patients with acute myeloid leukemia (AML). Measurable residual disease monitoring enhances risk stratification and may guide therapeutic intervention. The European LeukemiaNet working party recently came to a consensus recommendation incorporating leukemia associated immunophenotype-based different from normal approach by multi-color flow cytometry for measurable residual disease evaluation. However, the analytical approach is highly expertise-dependent and difficult to standardize. Here we demonstrate that loss of plasmacytoid dendritic cell differentiation after 7+3 induction in AML is highly specific for measurable residual disease positivity (specificity 97.4%) in a uniformly treated patient cohort. Moreover, loss of plasmacytoid dendritic cell differentiation as determined by a blast-to-plasmacytoid dendritic cell ratio >10 was strongly associated with inferior overall and relapse-free survival (RFS) [Hazard ratio 2.79, 95% confidence interval (95%CI): 0.98-7.97; P=0.077) and 3.83 (95%CI: 1.51-9.74; P=0.007), respectively), which is similar in magnitude to measurable residual disease positivity. Importantly, measurable residual disease positive patients who reconstituted plasmacytoid dendritic cell differentiation (blast/ plasmacytoid dendritic cell ratio <10) showed a higher rate of measurable residual disease clearance at later pre-transplant time points compared to patients with loss of plasmacytoid dendritic cell differentiation (blast/ plasmacytoid dendritic cell ratio <10) (6 of 12, 50% vs. 2 of 18, 11%; P=0.03). Furthermore pre-transplant plasmacytoid dendritic cell recovery was associated with superior outcome in measurable residual disease positive patients. Our study provides a novel, simple, broadly applicable, and quantitative multi-color flow cytometry approach to risk stratification in AML.

Genetic Hierarchy of Acute Myeloid Leukemia: From Clonal Hematopoiesis to Molecular Residual Disease

Recent advances in the field of cancer genome analysis revolutionized the picture we have of acute myeloid leukemia (AML). Pan-genomic studies, using either single nucleotide polymorphism arrays or whole genome/exome next generation sequencing, uncovered alterations in dozens of new genes or pathways, intimately connected with the development of leukemia. From a simple two-hit model in the late nineties, we are now building clonal stories that involve multiple unexpected cellular functions, leading to full-blown AML. In this review, we will address several seminal concepts that result from these new findings. We will describe the genetic landscape of AML, the association and order of events that define multiple sub-entities, both in terms of pathogenesis and in terms of clinical practice. Finally, we will discuss the use of this knowledge in the settings of new strategies for the evaluation of measurable residual diseases (MRD), using clone-specific multiple molecular targets.

Immunophenotypic measurable residual disease (MRD) in acute myeloid leukemia: Is multicentric MRD assessment feasible?

Flow-cytometric detection of now termed measurable residual disease (MRD) in acute myeloid leukemia (AML) has proven to have an independent prognostic impact. In a previous multicenter study we developed protocols to accurately define leukemia-associated immunophenotypes (LAIPs) at diagnosis. It has, however, not been demonstrated whether the use of the defined LAIPs in the same multicenter setting results in a high concordance between centers in MRD assessment. In the present paper we evaluated whether interpretation of list-mode data (LMD) files, obtained from MRD assessment of previously determined LAIPs during and after treatment, could reliably be performed in a multicenter setting. The percentage of MRD positive cells was simultaneously determined in totally 173 LMD files from 77 AML patients by six participating centers. The quantitative concordance between the six participating centers was meanly 84%, with slight variation of 75%-89%. In addition our data showed that the type and number of LAIPs were of influence on the performance outcome. The highest concordance was observed for LAIPs with cross-lineage expression, followed by LAIPs with an asynchronous antigen expression. Our results imply that immunophenotypic MRD assessment in AML will only be feasible when fully standardized methods are used for reliable multicenter assessment.

Measurable residual disease, conditioning regimen intensity, and age predict outcome of allogeneic hematopoietic cell transplantation for acute myeloid leukemia in first remission: A registry analysis of 2292 patients by the Acute Leukemia Working Party European Society of Blood and Marrow Transplantation

Patients with acute myeloid leukemia (AML) in morphological first complete remission (CR1) pre-allogeneic hematopoietic cell transplantation (HCT) may have measurable residual disease (MRD) by molecular and immunophenotyping criteria. We assessed interactions of MRD status with HCT conditioning regimen intensity in patients aged <50 years (y) or ≥50y. This was a retrospective study by the European Society for Blood and Marrow Transplantation registry. Patients were >18y with AML CR1 MRD NEG/POS and recipients of HCT in 2000-2015. Conditioning regimens were myeloablative (MAC), reduced intensity (RIC) or non-myeloablative (NMA). Outcomes included leukemia free survival (LFS), overall survival (OS), relapse incidence (RI), non-relapse mortality (NRM), chronic graft-vs-host (cGVHD), and GVHD-free and relapse-free survival (GRFS). The 2292 eligible patients were categorized into four paired groups: <50y MRD POS MAC (N = 240) vs RIC/NMA (N = 58); <50y MRD NEG MAC (N = 665) vs RIC/NMA (N = 195); ≥50y MRD POS MAC (N = 126) vs RIC/NMA (N = 230), and ≥50y MRD NEG MAC (N = 223) vs RIC/NMA (N = 555). In multivariate analysis RIC/NMA was only inferior to MAC for patients in the <50y MRD POS group, with worse RI (HR 1.71) and LFS (HR 1.554). Patients <50Y MRD NEG had less cGVHD after RIC/NMA HCT (HR 0.714). GRFS was not significantly affected by conditioning intensity in any group. Patients aged <50y with AML CR1 MRD POS status should preferentially be offered MAC allo-HCT. Prospective studies are needed to address whether patients with AML CR1 MRD NEG may be spared the toxicity of MAC regimens. New approaches are needed for ≥50y AML CR1 MRD POS.

Prognostic impact of t(16;21)(p11;q22) and t(16;21)(q24;q22) in pediatric AML: a retrospective study by the I-BFM Study Group

To study the prognostic relevance of rare genetic aberrations in acute myeloid leukemia (AML), such as t(16;21), international collaboration is required. Two different types of t(16;21) translocations can be distinguished: t(16;21)(p11;q22), resulting in the FUS-ERG fusion gene; and t(16;21)(q24;q22), resulting in RUNX1-core binding factor (CBFA2T3). We collected data on clinical and biological characteristics of 54 pediatric AML cases with t(16;21) rearrangements from 14 international collaborative study groups participating in the international Berlin-Frankfurt-Münster (I-BFM) AML study group. The AML-BFM cohort diagnosed between 1997 and 2013 was used as a reference cohort. RUNX1-CBFA2T3 (n = 23) had significantly lower median white blood cell count (12.5 × 10⁹/L, P = .03) compared with the reference cohort. FUS-ERG rearranged AML (n = 31) had no predominant French-American-British (FAB) type, whereas 76% of RUNX1-CBFA2T3 had an M1/M2 FAB type (M1, M2), significantly different from the reference cohort (P = .004). Four-year event-free survival (EFS) of patients with FUS-ERG was 7% (standard error [SE] = 5%), significantly lower compared with the reference cohort (51%, SE = 1%, P < .001). Four-year EFS of RUNX1-CBFA2T3 was 77% (SE = 8%, P = .06), significantly higher compared with the reference cohort. Cumulative incidence of relapse was 74% (SE = 8%) in FUS-ERG, 0% (SE = 0%) in RUNX1-CBFA2T3, compared with 32% (SE = 1%) in the reference cohort (P < .001). Multivariate analysis identified both FUS-ERG and RUNX1-CBFA2T3 as independent risk factors with hazard ratios of 1.9 (P < .0001) and 0.3 (P = .025), respectively. These results describe 2 clinically relevant distinct subtypes of pediatric AML. Similarly to other core-binding factor AMLs, patients with RUNX1-CBFA2T3 rearranged AML may benefit from stratification in the standard risk treatment, whereas patients with FUS-ERG rearranged AML should be considered high-risk.

Universal monitoring of minimal residual disease in acute myeloid leukemia

BACKGROUND

Optimal management of acute myeloid leukemia (AML) requires monitoring of treatment response, but minimal residual disease (MRD) may escape detection. We sought to identify distinctive features of AML cells for universal MRD monitoring.

METHODS

We compared genome-wide gene expression of AML cells from 157 patients with that of normal myeloblasts. Markers encoded by aberrantly expressed genes, including some previously associated with leukemia stem cells, were studied by flow cytometry in 240 patients with AML and in nonleukemic myeloblasts from 63 bone marrow samples.

RESULTS

Twenty-two (CD9, CD18, CD25, CD32, CD44, CD47, CD52, CD54, CD59, CD64, CD68, CD86, CD93, CD96, CD97, CD99, CD123, CD200, CD300a/c, CD366, CD371, and CX3CR1) markers were aberrantly expressed in AML. Leukemia-associated profiles defined by these markers extended to immature CD34+CD38- AML cells; expression remained stable during treatment. The markers yielded MRD measurements matching those of standard methods in 208 samples from 52 patients undergoing chemotherapy and revealed otherwise undetectable MRD. They allowed MRD monitoring in 129 consecutive patients, yielding prognostically significant results. Using a machine-learning algorithm to reduce high-dimensional data sets to 2-dimensional data, the markers allowed a clear visualization of MRD and could detect 1 leukemic cell among more than 100,000 normal cells.

CONCLUSION

The markers uncovered in this study allow universal and sensitive monitoring of MRD in AML. In combination with contemporary analytical tools, the markers improve the discrimination between leukemic and normal cells, thus facilitating data interpretation and, hence, the reliability of MRD results.

FUNDING

National Cancer Institute (CA60419 and CA21765); American Lebanese Syrian Associated Charities; National Medical Research Council of Singapore (1299/2011); Viva Foundation for Children with Cancer, Children's Cancer Foundation, Tote Board & Turf Club, and Lee Foundation of Singapore.

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.

Minimal/measurable residual disease in AML: a consensus document from the European LeukemiaNet MRD Working Party

Measurable residual disease (MRD; previously termed minimal residual disease) is an independent, postdiagnosis, prognostic indicator in acute myeloid leukemia (AML) that is important for risk stratification and treatment planning, in conjunction with other well-established clinical, cytogenetic, and molecular data assessed at diagnosis. MRD can be evaluated using a variety of multiparameter flow cytometry and molecular protocols, but, to date, these approaches have not been qualitatively or quantitatively standardized, making their use in clinical practice challenging. The objective of this work was to identify key clinical and scientific issues in the measurement and application of MRD in AML, to achieve consensus on these issues, and to provide guidelines for the current and future use of MRD in clinical practice. The work was accomplished over 2 years, during 4 meetings by a specially designated MRD Working Party of the European LeukemiaNet. The group included 24 faculty with expertise in AML hematopathology, molecular diagnostics, clinical trials, and clinical medicine, from 19 institutions in Europe and the United States.

Impact of post-transplant minimal residual disease on the clinical outcome of pediatric acute leukemia

This retrospective study examined the clinical significance of FCM-MRD in 36 patients with ALL and 29 patients with AML after their first allogeneic HSCT. Hematological (FCM-MRD ≥5.0%) and molecular relapse (FCM-MRD <5.0%) were first detected in 10 and two patients with ALL and in seven and eight patients with AML, respectively. Eight of 10 patients with molecular relapse eventually progressed to hematological relapse, although most were treated with immunological intervention by aggressive discontinuation of immunosuppressive therapy or donor lymphocyte infusion. Among these 12 patients, four of seven patients that obtained MRD^neg CR following post-transplant chemotherapy remain alive and disease-free after their second HSCT; however, all five patients who underwent a second HSCT in non-CR died of disease or treatment-related complications. As the FCM-MRD monitoring system used in the current study was probably not sensitive enough to detect MRD, which could be elucidated by immunological intervention, more sensitive diagnostic tools are mandatory for post-transplant MRD monitoring. Additional studies are required to address the impact of presecond transplant MRD on the clinical outcome of second HSCT.

Prognostic significance of flow-cytometry evaluation of minimal residual disease in children with acute myeloid leukaemia treated according to the AIEOP-AML 2002/01 study protocol

In children with acute myeloid leukaemia (AML), assessment of initial treatment response is an essential prognostic factor; methods more sensitive than morphology are still under evaluation. We report on the measurement of minimal residual disease (MRD), by multicolour flow-cytometry in one centralized laboratory, in 142 children with newly diagnosed AML enrolled in the Associazione Italiana di EmatoOncologia Pediatrica-AML 2002/01 trial. At the end of the first induction course, MRD was <0·1% in 69, 0·1-1% in 16 and >1% in 51 patients. The 8-year disease-free survival (DFS) of 125 children in morphological complete remission and with MRD <0·1%, 0·1-1% and ≥1% was 73·1 ± 5·6%, 37·8 ± 12·1% and 34·1 ± 8·8%, respectively (P < 0·01). MRD was also available after the second induction course in 92/142 patients. MRD was ≥0·1% at the end of the first induction course in 36 patients; 13 reached an MRD <0·1% after the second one and their DFS was 45·4 ± 16·7% vs. 22·8 ± 8·9% in patients with persisting MRD ≥0·1% (P = 0·037). Multivariate analysis demonstrated that MRD ≥0·1% after first induction course was, together with a monosomal karyotype, an independent adverse prognostic factor for DFS. Our results show that MRD detected by flow-cytometry after induction therapy predicts outcome in patients with childhood AML and can help stratifying post-remission treatment.

MRD in AML: does it already guide therapy decision-making?

Prognostic factors determined at diagnosis are predictive for outcome whereas achievement of morphological complete remission (CR) is still an important end point during treatment. Residual disease after therapy may reflect the sum of all diagnosis and postdiagnosis resistance mechanisms/factors; its measurement could hypothetically be very instrumental for guiding treatment. The possibility of defining residual disease (minimal residual disease [MRD]) far below the level of 5% blast cells is changing the landscape of risk classification. In this manuscript, the various methods, all different in sensitivity, specificity, and phase of development, to assess MRD are discussed. Currently, the 2 methods mostly used are flow cytometry-based immune MRD (multiparameter flow cytometry [MPFC]) and molecular MRD assessed by real-time quantitative polymerase chain reaction. Both have advantages and disadvantages that are summarized in detail. Many studies in children as well as adults already demonstrated that MRD detection by MPFC or molecular MRD provides strong prognostic information in acute myeloid leukemia (AML) after both induction and consolidation. These studies are summarized in this review. The general conclusion of this review is that a better definition of disease burden than morphological CR is now emerging. MRD assessed by flow or molecular techniques should become standard in every clinical trial in AML. Harmonization of antibody panels, introduction of single-cell tube systems (for determination of residual leukemic stem cells), and standardized analytical programs will pave the way for individual risk assessment and become a surrogate end point for survival in studies investigating new drugs, hopefully resulting in faster drug approval in AML.

Minimal Residual Disease in AML: Why Has It Lagged Behind Pediatric ALL?

Although the concept of minimal residual disease (MRD) as an indicator for the quality of treatment response is the same in acute myeloid leukemia (AML) and acute lymphoid leukemia (ALL), the practice of measuring MRD levels for monitoring response and guiding therapy after induction has been implemented much more rapidly in ALL, particularly pediatric ALL, than in AML. In this perspective we examine the facts and discuss why ALL appears to be more amenable to MRD-shaped risk allocation and a revised definition of complete remission.

Minimal Residual Disease and Childhood Leukemia: Standard of Care Recommendations From the Pediatric Oncology Group of Ontario MRD Working Group

Minimal residual disease (MRD) is an independent predictor of relapse risk in children with leukemia and is widely used for risk-adapted treatment. This article summarizes current evidence supporting the use of MRD, including clinical significance, current international clinical practice, impact statement, and recommended indications. The proposed MRD recommendations have been endorsed by the MRD Working Group of the Pediatric Oncology Group of Ontario and provide the foundation for a strategy that aims at equitable access to MRD evaluation for children with leukemia.

Residual disease detected by flow cytometry is an independent predictor of survival in childhood acute myeloid leukaemia; results of the NOPHO-AML 2004 study

Early response after induction is a prognostic factor for disease outcome in childhood acute myeloid leukaemia (AML). Residual disease (RD) detection by multiparameter flow cytometry (MFC) was performed at day 15 and before consolidation therapy in 101 patients enrolled in the Nordic Society of Paediatric Haemato-Oncology AML 2004 study. A multicentre laboratory approach to RD analysis was used. Event-free survival (EFS) and overall survival (OS) was significantly different in patients with and without RD at both time points, using a 0·1% RD cut-off level. RD-negative and -positive patients after first induction showed a 5-year EFS of 65 ± 7% and 22 ± 7%, respectively (P < 0·001) and an OS of 77 ± 6% (P = 0·025) and 51 ± 8%. RD-negative and -positive patients at start of consolidation therapy had a 5-year EFS of 57 ± 7% and 11 ± 7%, respectively (P < 0·001) and an OS of 78 ± 6% and 28 ± 11%) (P < 0·001). In multivariate analysis only RD was significantly correlated with survival. RD before consolidation therapy was the strongest independent prognostic factor for EFS [hazard ratio (HR):5·0; 95% confidence interval (CI):1·9-13·3] and OS (HR:7·0; 95%CI:2·0-24·5). In conclusion, RD before consolidation therapy identifies patients at high risk of relapse in need of intensified treatment. In addition, RD detection can be performed in a multicentre setting and can be implemented in future trials.

Bone Marrow Synoptic Reporting for Hematologic Neoplasms: Guideline From the College of American Pathologists Pathology and Laboratory Quality Center

CONTEXT

-There is ample evidence from the solid tumor literature that synoptic reporting improves accuracy and completeness of relevant data. No evidence-based guidelines currently exist for synoptic reporting for bone marrow samples.

OBJECTIVE

-To develop evidence-based recommendations to standardize the basic components of a synoptic report template for bone marrow samples.

DESIGN

-The College of American Pathologists Pathology and Laboratory Quality Center convened a panel of experts in hematopathology to develop recommendations. A systematic evidence review was conducted to address 5 key questions. Recommendations were derived from strength of evidence, open comment feedback, and expert panel consensus.

RESULTS

-Nine guideline statements were established to provide pathology laboratories with a framework by which to develop synoptic reporting templates for bone marrow samples. The guideline calls for specific data groups in the synoptic section of the pathology report; provides a list of evidence-based parameters for key, pertinent elements; and addresses ancillary testing.

CONCLUSION

-A framework for bone marrow synoptic reporting will improve completeness of the final report in a manner that is clear, succinct, and consistent among institutions.

Evolving Therapies in Acute Myeloid Leukemia: Progress at Last?

Acute myeloid leukemia (AML) is an acquired disease characterized by chromosomal translocations and somatic mutations that lead to leukemogenesis. Systemic combination chemotherapy with an anthracycline and cytarabine remains the standard induction regimen for "fit" adults. Patients who achieve complete remission generally receive postinduction therapy with cytarabine-based chemotherapy or an allogeneic bone marrow transplant. Those unfit for induction chemotherapy are treated with hypomethylating agents (HMAs), low-dose cytarabine, or they are offered supportive care alone with transfusions and prophylactic antimicrobials. The revolution in understanding the genetics of AML, facilitated by next-generation sequencing, has led to many new drugs against driver mutations. Better methods of identification of leukemic blasts have provided us with better means to detect the disease left behind after cytotoxic chemotherapy regimens. This measurable residual disease has been correlated with poorer relapse-free survival, demonstrating the need for novel strategies to eradicate it to improve the outcome of patients with acute leukemias. In this article, we discuss adapting and improving AML therapy by age and comorbidities, emerging targeted therapies in AML, and minimal residual disease (MRD) assessment in AML.

Minimal residual disease evaluation by flow cytometry is a complementary tool to cytogenetics for treatment decisions in acute myeloid leukaemia

The clinical utility of minimal residual disease (MRD) analysis in acute myeloid leukaemia (AML) is not yet defined. We analysed the prognostic impact of MRD level at complete remision after induction therapy using multiparameter flow cytometry in 306 non-APL AML patients. First, we validated the prognostic value of MRD-thresholds we have previously proposed (≥ 0.1%; ≥ 0.01-0.1%; and <0.01), with a 5-year RFS of 38%, 50% and 71%, respectively (p=0.002). Cytogenetics is the most relevant prognosis factor in AML, however intermediate risk cytogenetics represent a grey zone that require other biomarkers for risk stratification, and we show that MRD evaluation discriminate three prognostic subgroups (p=0.03). Also, MRD assessments yielded relevant information on favourable and adverse cytogenetics, since patients with favourable cytogenetics and high MRD levels have poor prognosis and patients with adverse cytogenetics but undetectable MRD overcomes the adverse prognosis. Interestingly, in patients with intermediate or high MRD levels, intensification with transplant improved the outcome as compared with chemotherapy, while the type of intensification therapy did not influenced the outcome of patients with low MRD levels. Multivariate analysis revealed age, MRD and cytogenetics as independent variables. Moreover, a scoring system, easy in clinical practice, was generated based on MRD level and cytogenetics.

Improved outcome of pediatric patients with acute megakaryoblastic leukemia in the AML-BFM 04 trial

Despite recent advances in the treatment of children with acute megakaryoblastic leukemia (AMKL) using intensified treatment protocols, clear prognostic indicators, and treatment recommendations for this acute myeloid leukemia (AML) subgroup are yet to be defined. Here, we report the outcome of 97 pediatric patients with de novo AMKL (excluding Down syndrome [DS]) enrolled in the prospective multicenter studies AML-BFM 98 and AML-BFM 04 (1998-2014). AMKL occurred in 7.4 % of pediatric AML cases, at younger age (median 1.44 years) and with lower white blood cell count (mean 16.5 × 10⁹/L) as compared to other AML subgroups. With 60 ± 5 %, children with AMKL had a lower 5-year overall survival (5-year OS; vs. 68 ± 1 %, P_{log rank} = 0.038). Yet, we achieved an improved 5-year OS in AML-BFM 04 compared to AML-BFM 98 (70 ± 6 % vs. 45 ± 8 %, P_{log rank} = 0.041). Allogeneic hematopoietic stem cell transplantation in first remission did not provide a significant survival benefit (5-year OS 70 ± 11 % vs. 63 ± 6 %; P_Mantel-Byar = 0.85). Cytogenetic data were available for n = 78 patients. AMKL patients with gain of chromosome 21 had a superior 5-year OS (80 ± 9 %, P_{log rank} = 0.034), whereas translocation t(1;22)(p13;q13) was associated with an inferior 5-year event-free survival (38 ± 17 %, P_{log rank} = 0.04). However, multivariate analysis showed that treatment response (bone marrow morphology on day 15 and 28) was the only independent prognostic marker (RR = 4.39; 95 % CI, 1.97–9.78). Interestingly, GATA1-mutations were detected in six patients (11 %) without previously known trisomy 21. Thus, AMKL (excluding DS) remains an AML subgroup with inferior outcome. Nevertheless, with intensive therapy regimens, a steep increase in the survival rates was achieved.

Prospective validation of a new method of monitoring minimal residual disease in childhood acute myelogenous leukemia

PURPOSE

This study evaluated the prognostic impact of a novel, simple, and standardized assay for monitoring minimal residual disease (MRD) in pediatric acute myelogenous leukemia (AML).

EXPERIMENTAL DESIGN

The expression of seven leukemia-associated genes (WT1, PRAME, CCL23, GAGED2, MSLN, SPAG6, and ST18) was measured by TaqMan Low Density Arrays in 112 patients and 52 healthy controls. Patients were treated according to the multicenter study AML-BFM 2004. Samples were collected prospectively at standard time points. The laboratory that measured MRD was blinded to patient outcome.

RESULTS

Relapse-free survival (RFS) was 95% (N = 19; SE = 5%) if expression of all genes was down to normal on day 15, 63% (N = 41; SE = 8%) if expression was normalized on day 28, and 38% (N = 21; SE = 11%) in patients who still showed elevated expression on day 28. The prognostic impact of MRD remained significant (P = 0.002) when patients were stratified for the AML-BFM 2004 risk group. Multivariate analysis identified the MRD risk group and day 28 cytology as the only independent prognostic factors. Patients with a cytologic nonremission on day 28, which was confirmed by MRD, had a dismal prognosis. Only 1 out of 8 patients survived without relapse.

CONCLUSIONS

This novel method of monitoring MRD has a strong prognostic impact that is independent from established risk factors in childhood AML.