Advancing the Minimal Residual Disease Concept in Acute Myeloid Leukemia

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.

Highlighting the Prognostic Importance of Measurable Residual Disease Among Acute Myeloid Leukemia Risk Factors

Objective:

The optimal timing of measurable residual disease (MRD) evaluation in acute myeloid leukemia (AML) patients has not been well defined yet. We aimed to investigate the impact of MRD in pre- and post-allogeneic hematopoietic stem cell transplantation (AHSCT) periods on prognostic parameters.

Materials and Methods:

Seventy-seven AML patients who underwent AHSCT in complete morphological remission were included. MRD analyses were performed by 10-color MFC and 10^-4 was defined as positive. Relapse risk and survival outcomes were assessed based on pre- and post-AHSCT MRD positivity.

Results:

The median age of the patients was 46 (range: 18-71) years, and 41 (53.2%) were male while 36 (46.8%) were female. The median follow-up after AHSCT was 12.2 months (range: 0.2-73.0). The 2-year overall survival (OS) in the entire cohort was 37.0%, with a significant difference between patients who were MRD-negative and MRD-positive before AHSCT, estimated as 63.0% versus 16.0%, respectively (p=0.005). MRD positivity at +28 days after AHSCT was also associated with significantly inferior 2-year OS when compared to MRD negativity (p=0.03). The risk of relapse at 1 year was 2.4 times higher (95% confidence interval: 1.1-5.6; p=0.04) in the pre-AHSCT MRD-positive group when compared to the MRD-negative group regardless of other transplant-related factors, including pre-AHSCT disease status (i.e., complete remission 1 and 2). Event-free survival (EFS) was significantly shorter in patients who were pre-AHSCT MRD-positive (p=0.016). Post-AHSCT MRD positivity was also related to an increased relapse risk. OS and EFS were significantly inferior among MRD-positive patients at +28 days after AHSCT (p=0.03 and p=0.019).

Conclusion:

Our results indicate the importance of MRD before and after AHSCT independently of other factors.

Detection of Fusion Genes to Determine Minimal Residual Disease in Leukemia Using Next-Generation Sequencing

Background

Measuring minimal residual disease (MRD), the persistence of leukemic cells after treatment, is important for monitoring leukemia recurrence. The current methods for monitoring MRD are flow cytometry, to assess aberrant immune phenotypes, and digital droplet PCR (ddPCR), to target genetic aberrations such as single-nucleotide variants and gene fusions. We present the performance of an RNA-based next-generation sequencing (NGS) method for MRD gene fusion detection compared with ddPCR. This method may have advantages, including the capacity to analyze different genetic aberrations and patients in 1 experiment. In particular, detection at the RNA level may be highly sensitive if the genetic aberration is highly expressed.

Methods

We designed a probe-based NGS panel targeting the breakpoints of 11 fusion genes previously identified in clinical patients and 2 fusion genes present in cell lines. Blocking probes were added to prevent nonspecific enrichment. Each patient RNA sample was diluted in background RNA, depleted for rRNA and globin mRNA, converted to cDNA, and prepared for sequencing. Unique sequence reads, identified by unique molecular identifiers, were aligned directly to reference transcripts. The same patient and cell-line samples were also analyzed with ddPCR for direct comparison.

Results

Our NGS method reached a maximum sensitivity of 1 aberrant cell in 10 000 cells and was mostly within a factor of 10 compared with ddPCR.

Conclusions

Our detection limit was below the threshold of 1:1000 recommended by European Leukemia Net. Further optimizations are easy to implement and are expected to boost the sensitivity of our method to diagnostically obtained ddPCR thresholds.

Next-generation sequencing for measurable residual disease detection in acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a blood cancer characterized by acquired genetic mutations. There is great interest in accurately establishing measurable residual disease (MRD) burden in AML patients in remission after treatment but at risk of relapse. However, inter- and intrapatient genetic diversity means that, unlike in the chronic myeloid and acute promyelocytic leukaemias, no single genetic abnormality is pathognomonic for all cases of AML MRD. Next-generation sequencing offers the opportunity to test broadly and deeply for potential genetic evidence of residual AML, and while not currently accepted for such use clinically, is likely to be increasingly used for AML MRD testing in the future.

CD34+CD38- leukemic stem cell frequency to predict outcome in acute myeloid leukemia

Current risk algorithms are primarily based on pre-treatment factors and imperfectly predict outcome in acute myeloid leukemia (AML). We introduce and validate a post-treatment approach of leukemic stem cell (LSC) assessment for prediction of outcome. LSC containing CD34+CD38- fractions were measured using flow cytometry in an add-on study of the HOVON102/SAKK trial. Predefined cut-off levels were prospectively evaluated to assess CD34+CD38-LSC levels at diagnosis (n = 594), and, to identify LSC^low/LSC^high (n = 302) and MRD^low/MRD^high patients (n = 305) in bone marrow in morphological complete remission (CR). In 242 CR patients combined MRD and LSC results were available. At diagnosis the CD34⁺CD38^- LSC frequency independently predicts overall survival (OS). After achieving CR, combining LSC and MRD showed reduced survival in MRD^high/LSC^high patients (hazard ratio [HR] 3.62 for OS and 5.89 for cumulative incidence of relapse [CIR]) compared to MRD^low/LSC^high, MRD^high/LSC^low, and especially MRD^low/LSC^low patients. Moreover, in the NPM1mutant positive sub-group, prognostic value of golden standard NPM1-MRD by qPCR can be improved by addition of flow cytometric approaches. This is the first prospective study demonstrating that LSC strongly improves prognostic impact of MRD detection, identifying a patient subgroup with an almost 100% treatment failure probability, warranting consideration of LSC measurement incorporation in future AML risk schemes.

Acute myeloid leukaemia

For several decades, few substantial therapeutic advances have been made for patients with acute myeloid leukaemia. However, since 2017 unprecedented growth has been seen in the number of drugs available for the treatment of acute myeloid leukaemia, with several new drugs receiving regulatory approval. In addition to advancing our therapeutic armamentarium, an increased understanding of the biology and genomic architecture of acute myeloid leukaemia has led to refined risk assessment of this disease, with consensus risk stratification guidelines now incorporating a growing number of recurrent molecular aberrations that aid in the selection of risk-adapted management strategies. Despite this promising recent progress, the outcomes of patients with acute myeloid leukaemia remain unsatisfactory, with more than half of patients ultimately dying from their disease. Enrolment of patients into clinical trials that evaluate novel drugs and rational combination therapies is imperative to continuing this progress and further improving the outcomes of patients with acute myeloid leukaemia.

The Prognostic Significance of Measurable ("Minimal") Residual Disease in Acute Myeloid Leukemia

PURPOSE OF REVIEW

The purpose of this review was to evaluate recent literature on detection methodologies for, and prognostic significance of, measurable ("minimal") residual disease (MRD) in acute myeloid leukemia (AML).

RECENT FINDINGS

There is no "one-fits-all" approach to MRD testing in AML. Most exploited to date are methods relying on immunophenotypic aberrancies (identified via multiparameter flow cytometry) or genetic abnormalities (identified via PCR-based assays). Current methods have important shortcomings, including the lack of assay platform standardization/harmonization across laboratories. In parallel to refinements of existing technologies and data analysis/interpretation, new methodologies (e.g., next-generation sequencing-based assays) are emerging that eventually may complement or replace existing ones. This dynamic evolution of MRD testing has complicated comparisons between individual studies. Nonetheless, an ever-growing body of data demonstrates that a positive MRD test at various time points throughout chemotherapy and hematopoietic cell transplantation identifies patients at particularly high risks of disease recurrence and short survival even after adjustment for other risk factors.

Should patients with acute myeloid leukemia and measurable residual disease be transplanted in first complete remission?

PURPOSE OF REVIEW

Measurable ('minimal') residual disease in acute myeloid leukemia during first complete morphologic remission (MRD CR1) identifies patients with particularly high relapse risk and short survival. Here, we examine the evidence regarding optimal postremission treatment strategy for such patients.

RECENT FINDINGS

With chemotherapy alone or chemotherapy/autologous hematopoietic cell transplantation (HCT), disease recurrence appears inevitable in patients with MRD CR1. Nonrandomized studies indicate that allogeneic HCT improves outcomes over chemotherapy and/or autologous HCT, although relapse risks remain substantial. Emerging data suggest that myeloablative cord blood HCT may overcome the negative impact of MRD to a greater degree than other transplants, but the relative contributions of intensified conditioning and stem cell source to this effect are unknown.

SUMMARY

Available evidence supports the recommendation to consider allogeneic HCT for all acute myeloid leukemia patients in MRD CR1. Whether cord blood transplants should be prioritized deserves further investigation. To what degree outcomes of MRD CR1 patients could be improved by treatment intensification during induction, postremission therapy and/or before transplantation to revert the patient into an MRD state is currently unknown, as is the value of post-transplant preemptive therapies. These remain areas worthy of investigation, preferably in the setting of controlled clinical trials.

State of the Art Update and Next Questions: Acute Myeloid Leukemia

As our general understanding regarding the complex nature of acute myeloid leukemia (AML) is expanding, so is our ability to translate this biological data into clinically relevant information. The use of whole genome and whole exome sequencing has begun to shed light on the importance of a variety of somatic mutations that are frequently identified in AML. In turn, this has allowed the field to incorporate mutational data into prognostic classifications which can guide treatment decisions. Furthermore, minimal residual disease (MRD) monitoring in AML is more commonplace as the prognostic relevance of MRD at various time points during treat is becoming clear. Many novel treatments have recently been approved, or are expected to gain approval in the near future, and this is opening the door to a more personalized approach to the management of AML.

Technical Advances in the Measurement of Residual Disease in Acute Myeloid Leukemia

Outcomes for those diagnosed with acute myeloid leukemia (AML) remain poor. It has been widely established that persistent residual leukemic burden, often referred to as measurable or minimal residual disease (MRD), after induction therapy or at the time of hematopoietic stem cell transplant (HSCT) is highly predictive for adverse clinical outcomes and can be used to identify patients likely to experience clinically evident relapse. As a result of inherent genetic and molecular heterogeneity in AML, there is no uniform method or protocol for MRD measurement to encompass all cases. Several techniques focusing on identifying recurrent molecular and cytogenetic aberrations or leukemia-associated immunophenotypes have been described, each with their own strengths and weaknesses. Modern technologies enabling the digital quantification and tracking of individual DNA or RNA molecules, next-generation sequencing (NGS) platforms, and high-resolution imaging capabilities are among several new avenues under development to supplement or replace the current standard of flow cytometry. In this review, we outline emerging modalities positioned to enhance MRD detection and discuss factors surrounding their integration into clinical practice.

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.

Measurable residual disease testing in acute myeloid leukaemia

There is considerable interest in developing techniques to detect and/or quantify remaining leukaemia cells termed measurable or, less precisely, minimal residual disease (MRD) in persons with acute myeloid leukaemia (AML) in complete remission defined by cytomorphological criteria. An important reason for AML MRD-testing is the possibility of estimating the likelihood (and timing) of leukaemia relapse. A perfect MRD-test would precisely quantify leukaemia cells biologically able and likely to cause leukaemia relapse within a defined interval. AML is genetically diverse and there is currently no uniform approach to detecting such cells. Several technologies focused on immune phenotype or cytogenetic and/or molecular abnormalities have been developed, each with advantages and disadvantages. Many studies report a positive MRD-test at diverse time points during AML therapy identifies persons with a higher risk of leukaemia relapse compared with those with a negative MRD-test even after adjusting for other prognostic and predictive variables. No MRD-test in AML has perfect sensitivity and specificity for relapse prediction at the cohort- or subject levels and there are substantial rates of false-positive and -negative tests. Despite these limitations, correlations between MRD-test results and relapse risk have generated interest in MRD-test result-directed therapy interventions. However, convincing proof that a specific intervention will reduce relapse risk in persons with a positive MRD-test is lacking and needs testing in randomized trials. Routine clinical use of MRD-testing requires further refinements and standardization/harmonization of assay platforms and results reporting. Such data are needed to determine whether results of MRD-testing can be used as a surrogate end point in AML therapy trials. This could make drug-testing more efficient and accelerate regulatory approvals. Although MRD-testing in AML has advanced substantially, much remains to be done.

Effect of granulocyte colony-stimulating factor on outcomes in patients with non-M3 acute myelogenous leukemia treated with anthracycline-based induction (7+3 regimen) chemotherapies

We analyzed the effects of granulocyte colony-stimulating factor (G-CSF) on outcomes in 315 anthracycline-based induction chemotherapy-treated patients with non-M3 acute myelogenous leukemia (AML). Patients were classified as follows: no G-CSF administration during induction (no G-CSF group; 112 patients); administration immediately upon neutropenia onset (absolute neutrophil counts (ANC)<1000/μL), but before febrile neutropenia (preemptive group; 74 patients); and administration following febrile neutropenia development (therapeutic group; 129 patients). G-CSF users had a shorter time to ANC recovery than the no G-CSF group (p<0.001). The chemotherapy-induced febrile neutropenia (CIFN) duration was significantly shorter in the preemptive group than in other groups (p<0.001). The incidence of CIFN was not significantly different between preemptive and non-G-CSF users (84.8% versus 82.4%). Preemptive G-CSF administration modestly improved treatment-related mortality (TRM), compared with no G-CSF administration (p=0.076 in multivariate analysis). G-CSF administration did not affect relapse-free or overall survivals or the cumulative relapse incidence among the groups. In conclusion, preemptive G-CSF administration reduced CIFN duration and modestly improved TRM without affecting chemotherapy outcomes. These effects were not observed in the therapeutic group; therefore, initiation of G-CSF during induction therapy before the development of febrile neutropenia may be desirable.

Bone marrow evaluation for diagnosis and monitoring of acute myeloid leukemia

The diagnosis of acute myeloid leukemia (AML) can be made based on peripheral blood or bone marrow blasts. In this review, we will discuss the role of bone marrow evaluation and peripheral blood monitoring in the diagnosis, management, and follow up of AML patients. For patients with circulating blasts, it is reasonable to perform the necessary studies needed for diagnosis and risk stratification, including multiparametric flow cytometry, cytogenetics, and molecular analysis, on a peripheral blood specimen. The day 14 marrow is used to document hypocellularity in response to induction chemotherapy, but it is unclear if that assessment is necessary as it often does not affect immediate management. Currently, response assessments performed at count recovery for evaluation of remission and measurable residual disease rely on bone marrow sampling. For monitoring of relapse, peripheral blood evaluation may be adequate, but the sensitivity of bone marrow testing is in some cases superior. While bone marrow evaluation can certainly be avoided in particular situations, this cumbersome and uncomfortable procedure currently remains the de facto standard for response assessment.

Minimal residual disease prior to allogeneic hematopoietic cell transplantation in acute myeloid leukemia: a meta-analysis

Minimal residual disease prior to allogeneic hematopoietic cell transplantation has been associated with increased risk of relapse and death in patients with acute myeloid leukemia, but detection methodologies and results vary widely. We performed a systematic review and meta-analysis evaluating the prognostic role of minimal residual disease detected by polymerase chain reaction or multiparametric flow cytometry before transplant. We identified 19 articles published between January 2005 and June 2016 and extracted hazard ratios for leukemia-free survival, overall survival, and cumulative incidences of relapse and non-relapse mortality. Pre-transplant minimal residual disease was associated with worse leukemia-free survival (hazard ratio=2.76 [1.90-4.00]), overall survival (hazard ratio=2.36 [1.73-3.22]), and cumulative incidence of relapse (hazard ratio=3.65 [2.53-5.27]), but not non-relapse mortality (hazard ratio=1.12 [0.81-1.55]). These associations held regardless of detection method, conditioning intensity, and patient age. Adverse cytogenetics was not an independent risk factor for death or relapse. There was more heterogeneity among studies using flow cytometry-based than WT1 polymerase chain reaction-based detection (I²=75.1% vs. <0.1% for leukemia-free survival, 67.8% vs. <0.1% for overall survival, and 22.1% vs. <0.1% for cumulative incidence of relapse). These results demonstrate a strong relationship between pre-transplant minimal residual disease and post-transplant relapse and survival. Outcome heterogeneity among studies using flow-based methods may underscore site-specific methodological differences or differences in test performance and interpretation.

Targeted therapies in the treatment of adult acute myeloid leukemias: current status and future perspectives

The rapid advancement of next-generation sequencing techniques and the identification of molecular driver events responsible for leukemia development are opening the door to new pharmacologic-targeted agents to tailor treatment of acute myeloid leukemia (AML) in individual patients. However, the use of targeted therapies in AML has met with only modest success. Molecular studies have identified AML subsets characterized by driver mutational events, such as NPM1, FLT3-ITD and IDH1-2 mutations, and have provided preclinical evidence that the targeting of these mutant molecules could represent a valuable therapeutic strategy. Recent studies have provided the first pieces of evidence that FLT3 targeting in FLT3-mutant AMLs, IDH1/2 inhibition in IDH-mutant AMLs and targeting membrane molecules preferentially expressed on leukemic progenitor/stem cells, such as CD33 and CD123, represent a clinically valuable strategy.

Multigene Measurable Residual Disease Assessment Improves Acute Myeloid Leukemia Relapse Risk Stratification in Autologous Hematopoietic Cell Transplantation

We report here the largest study to date of adult patients with acute myeloid leukemia (AML) tested for measurable residual disease (MRD) at the time of autologous hematopoietic cell transplantation (auto-HCT). Seventy-two adult patients who underwent transplantation between 2004 and 2013 at a single academic medical center (University of California San Francisco) were eligible for this retrospective study based on availability of cryopreserved granulocyte colony-stimulating factor (GCSF)-mobilized autologous peripheral blood progenitor cell (PBPC) leukapheresis specimens ("autografts"). Autograft MRD was assessed by molecular methods (real-time quantitative PCR [RQ-PCR] for Wilms tumor 1 (WT1) alone or a multigene panel) and by multiparameter flow cytometry (MPFC). WT1 RQ-PCR testing of the autograft had low sensitivity for relapse prediction (14%) and a negative predictive value of 51%. MPFC failed to identify MRD in any of 34 autografts tested. Combinations of molecular MRD assays, however, improved prediction of post-auto-HCT relapse. In multivariate analysis of clinical variables, including age, gender, race, cytogenetic risk category, and CD34⁺ cell dose, only autograft multigene MRD as assessed by RQ-PCR was statistically significantly associated with relapse. One year after transplantation, only 28% patients with detectable autograft MRD were relapse free, compared with 67% in the MRD-negative cohort. Multigene MRD, while an improvement on other methods tested, was however suboptimal for relapse prediction in unselected patients, with specificity of 83% and sensitivity of 46%. In patients with known chromosomal abnormalities or mutations, however, better predictive value was observed with no relapses observed in MRD-negative patients in the first year after auto-HCT compared with 83% incidence of relapse in the MRD-positive patients (hazard ratio, 12.45; P = .0016). In summary, increased personalization of MRD monitoring by use of a multigene panel improved the ability to risk stratify patients for post-auto-HCT relapse. WT1 RQ-PCR and flow cytometric assessment for AML MRD in autograft samples had limited value for predicting relapse after auto-HCT. We demonstrate that cryopreserved autograft material presents unique challenges for AML MRD testing because of the masking effects of previous GCSF exposure on gene expression and flow cytometry signatures. In the absence of information regarding diagnostic characteristics, sources other than GCSF-stimulated PBSC leukapheresis specimens should be considered as alternatives for MRD testing in AML patients undergoing auto-HCT.

Incorporating measurable ('minimal') residual disease-directed treatment strategies to optimize outcomes in adults with acute myeloid leukemia

Curative-intent therapy leads to complete remissions in many adults with acute myeloid leukemia (AML), but relapse remains common. Numerous studies have unequivocally demonstrated that the persistence of measurable ('minimal') residual disease (MRD) at the submicroscopic level during morphologic remission identifies patients at high risk of disease recurrence and short survival. This association has provided the impetus to customize anti-leukemia therapy based on MRD data, a strategy that is now routinely pursued in acute promyelocytic leukemia (APL). While it is currently uncertain whether this approach will improve outcomes in AML other than APL, randomized studies have validated MRD-based risk-stratified treatment algorithms in acute lymphoblastic leukemia. Here, we review the available studies examining MRD-directed therapy in AML, appraise their strengths and limitations, and discuss avenues for future investigation.

Plasma-derived exosomes in acute myeloid leukemia for detection of minimal residual disease: are we ready?

The recent emergence of plasma-derived exosomes as biomarkers of leukemic relapse has introduced the potential for more sensitive non-invasive monitoring of leukemia patients based on the molecular and genetic analysis of the exosome cargo. In principle, the protein, lipid, miRNA, mRNA or DNA profiles of exosomes in patients' plasma that associate with leukemic relapse can be identified. The diagnostic/prognostic value of these profiles could then be validated in prospective clinical studies. Here, we consider the potential of exosomes to fulfill the role of future biomarkers of minimal residual disease in AML. The rationale for developing exosome-based methodology for minimal residual disease detection is based on promising early observations. However, standards need to be established for evaluating exosome identity, isolation from body fluids, and assessment methods. The rapidly expanding knowledge of the exosome biology suggests that the exosome status as potential biomarkers may become clarified in the near future.

Pre- and post-transplant quantification of measurable ('minimal') residual disease via multiparameter flow cytometry in adult acute myeloid leukemia

Measurable (“minimal”) residual disease (MRD) before or after hematopoietic cell transplantation (HCT) identifies adults with AML at risk of poor outcomes. Here, we studied whether peri-transplant MRD dynamics can refine risk assessment. We analyzed 279 adults receiving myeloablative allogeneic HCT in first or second remission who survived at least 35 days and underwent 10-color multiparametric flow cytometry (MFC) analyses of marrow aspirates before and 28±7 days after transplantation. MFC-detectable MRD before (n=63) or after (n=16) transplantation identified patients with high relapse risk and poor survival. Forty-nine patients cleared MRD with HCT conditioning, whereas 2 patients developed new evidence of disease. The 214 MRD^neg/MRD^neg patients had excellent outcomes, whereas both MRD^neg/MRD^pos patients died within 100 days following transplantation. For patients with pre-HCT MRD, outcomes were poor regardless of post-HCT MRD status, although survival beyond 3 years was observed among the 58 patients with decreasing but not the 7 patients with increasing peri-HCT MRD levels. In multivariable models, pre-HCT but not post-HCT MRD was independently associated with OS and RR. These data indicate that MRD^pos patients before transplantation have a high relapse risk regardless of whether or not they clear MFC-detectable disease with conditioning and should be considered for pre-emptive therapeutic strategies.

Monitoring minimal residual disease in acute myeloid leukaemia: a review of the current evolving strategies

Several disease-monitoring techniques are available for the physician treating acute myeloid leukaemia (AML). Besides immunohistochemistry assisted light microscopy, the past 20 years have seen the development and preclinical perfection of a number of techniques, most notably quantitative polymerase chain reaction (PCR) and multicolor flow cytometry. Late additions to the group of applicable assays include next generation sequencing and digital PCR. In this review the principles of use of these modalities at three different time points during the AML disease course are discussed, namely at the time of treatment evaluation, pretransplantation and postconsolidation. The drawbacks and pitfalls of each different technique are delineated. The evidence or lack of evidence for minimal residual disease guided treatment decisions is discussed. Lastly, future strategies in the MRD field are suggested and commented upon.

Should acute myeloid leukemia patients with actionable targets be offered investigational treatment after failing one cycle of standard induction therapy?

PURPOSE OF REVIEW

Therapeutic failure in acute myeloid leukemia remains common. It may be advantageous to identify patients with suboptimal treatment responses early as they may benefit from timely care strategy changes. Here, responses portending failure of standard induction therapy are reviewed and therapeutic options examined, including use of investigational, targeted agents for suitable patients.

RECENT FINDINGS

Patients entering complete remission without minimal residual disease early, that is, with one cycle of standard induction chemotherapy, have a lower relapse risk and live longer than other similarly-treated patients, supporting the proposition of early complete remission without minimal residual disease as a criterion for induction therapy success. Investigational small molecule drugs are appealing for patients who fail standard therapies, but complete remission rates as a single agent are typically modest.

SUMMARY

The relative value of different treatment strategies if a first standard induction therapy cycle fails to produce complete remission is unknown. However, retreatment with the same therapy often leads to complete remission and provides a benchmark against which other approaches should be compared. Addition of investigational small molecule drugs to standard reinduction therapy in patients with actionable targets could offer an attractive therapeutic strategy in this situation that might improve outcomes and facilitate clinical drug testing.

Precision medicine for acute myeloid leukemia

The goal of precision medicine is to personalize therapy based on individual patient variation, to correctly select the right treatment, for the right patient, at the right time. Acute myeloid leukemia (AML) is a heterogeneous collection of myeloid malignancies with diverse genetic etiology and the potential for intra-patient clonal evolution over time. We discuss here how the precision medicine paradigm might be applied to the care of AML patients by focusing on the potential roles of targeting therapy by patient-specific somatic mutations and aberrant pathways, ex-vivo drug sensitivity and resistance testing, high sensitivity measurements of residual disease burden and biology along with potential clinical trial and regulatory constraints.