Excellent outcome of minimal residual disease-defined low-risk patients is sustained with more than 10 years follow-up: results of UK paediatric acute lymphoblastic leukaemia trials 1997-2003

Single-cell DNA and surface protein characterization of high hyperdiploid acute lymphoblastic leukemia at diagnosis and during treatment

High hyperdiploid (HeH) B-cell acute lymphoblastic leukemia (B-ALL) is the most prevalent subtype of childhood ALL. This leukemia is characterized by trisomies and tetrasomies of specific chromosomes and additional point mutations. Here, we used single-cell targeted DNA and antibody sequencing to determine the clonal evolution of HeH B-ALL during development and chemotherapy treatment. Chromosomal copy number changes were mostly stable over all the leukemia cells, while mutations were typically subclonal. Within all 13 cases, at least one RAS mutant (KRAS or NRAS) subclone was detected (range: 1 to 4 subclones with RAS mutations), indicating the importance of RAS signaling in HeH B-ALL development. NSD2 mutations were detected in 4 out of 13 cases and always in a subclone with RAS signaling mutations. Single-cell DNA sequencing detected residual leukemia cells during chemotherapy treatment, and analysis of chromosomal copy number changes aided in the accurate detection of these cells. Our single-cell data demonstrate that chromosomal changes are acquired prior to additional mutations and that RAS signaling mutations are present in all HeH cases, often as subclonal mutations. This single-cell multi-omics study enabled us to extensively characterize the genetic and surface protein heterogeneity in patients with HeH B-ALL.

The Prognostic Effect of IKZF1 Deletions in ETV6::RUNX1 and High Hyperdiploid Childhood Acute Lymphoblastic Leukemia

IKZF1 deletions are an established prognostic factor in childhood acute lymphoblastic leukemia (ALL). However, their relevance in patients with good risk genetics, namely ETV6::RUNX1 and high hyperdiploid (HeH), ALL remains unclear. We assessed the prognostic impact of IKZF1 deletions in 939 ETV6::RUNX1 and 968 HeH ALL patients by evaluating data from 16 trials from 9 study groups. Only 3% of ETV6::RUNX1 cases (n = 26) were IKZF1-deleted; this adversely affected survival combining all trials (5-year event-free survival [EFS], 79% versus 92%; P = 0.02). No relapses occurred among the 14 patients with an IKZF1 deletion treated on a minimal residual disease (MRD)-guided protocols. Nine percent of HeH cases (n = 85) had an IKZF1 deletion; this adversely affected survival in all trials (5-year EFS, 76% versus 89%; P = 0.006) and in MRD-guided protocols (73% versus 88%; P = 0.004). HeH cases with an IKZF1 deletion had significantly higher end of induction MRD values (P = 0.03). Multivariate Cox regression showed that IKZF1 deletions negatively affected survival independent of sex, age, and white blood cell count at diagnosis in HeH ALL (hazard ratio of relapse rate [95% confidence interval]: 2.48 [1.32-4.66]). There was no evidence to suggest that IKZF1 deletions affected outcome in the small number of ETV6::RUNX1 cases in MRD-guided protocols but that they are related to higher MRD values, higher relapse, and lower survival rates in HeH ALL. Future trials are needed to study whether stratifying by MRD is adequate for HeH patients or additional risk stratification is necessary.

Impact of minimal residual disease on relapse in childhood acute lymphoblastic leukemia: Lessons learnt from a tertiary cancer center in India

Prognostic predictive value of end of induction minimal residual disease (EOI-MRD) is well established in acute lymphoblastic leukemia (ALL). We evaluated the factors likely to affect EOI-MRD positivity (>0.01%) by flow cytometry and relapse in different BFM-95 (Berlin-Frankfurt-Munich) risk groups among children and adolescents. In this retrospective study, data of 223 newly diagnosed patients with ALL was analyzed. Association between demographic and pretreatment characteristics with EOI-MRD was assessed. Risk factors for relapse were analyzed using univariate and multivariate Cox regression. Proportion of the SR (standard risk), MR (moderate risk), and HR (high risk) patients was 18.8%, 60.9%, 20.3%, respectively. Positive EOI-MRD among these risk groups was observed in 11.9%, 18.3%, and 55.5% patients respectively (p value <.01%). MRD positivity was more likely to be associated with older age (>10 years) and BFM-HR patients (p value .0008 and <.0001). Thirty-four (15.2%) patients relapsed in the whole cohort. On univariate analysis, statistically significant factors for RFS (relapse-free survival) included hyperleukocytosis, high-risk cytogenetics, NCI (National Cancer Institute) high risk, poor day-8 prednisolone response, BFM-HR and positive EOI-MRD status. Of all these only EOI-MRD retained its impact by multivariate analysis. Positive EOI-MRD significantly predicted relapse in BFM-MR with 5-year RFS of 88.0% and 68.4% (p value .02). Five-year RFS of EOI-MRD negative and positive groups were 86.4% and 65.5%, respectively (p value .004). EOI-MRD is a powerful tool to predict relapse in children and adolescent with ALL especially in BFM-MR. Application of MRD in HR patients needs to be redefined in conjunction with other variables.

Outcomes of Childhood Noninfant Acute Lymphoblastic Leukemia With 11q23/KMT2A Rearrangements in a Modern Therapy Era: A Retrospective International Study

PURPOSE

We aimed to study prognostic factors and efficacy of allogeneic hematopoietic stem-cell transplantation (allo-HSCT) in first remission of patients with noninfant childhood acute lymphoblastic leukemia (ALL) with 11q23/KMT2A rearrangements treated with chemotherapy regimens between 1995 and 2010.

PATIENTS AND METHODS

Data were retrospectively retrieved from 629 patients with 11q23/KMT2A-rearranged ALL from 17 members of the Ponte-di-Legno Childhood ALL Working Group. Clinical and biologic characteristics, early response assessed by minimal residual disease at the end of induction (EOI) therapy, and allo-HSCT were analyzed for their impact on outcomes.

RESULTS

A specific 11q23/KMT2A translocation partner gene was identified in 84.3% of patients, with the most frequent translocations being t(4;11)(q21;q23) (n = 273; 51.5%), t(11;19)(q23;p13.3) (n = 106; 20.0%), t(9;11)(p21_22;q23) (n = 76; 14.3%), t(6;11)(q27;q23) (n = 20; 3.8%), and t(10;11)(p12;q23) (n = 14; 2.6%); 41 patients (7.7%) had less frequently identified translocation partner genes. Patient characteristics and early response varied among subgroups, indicating large biologic heterogeneity and diversity in therapy sensitivity among 11q23/KMT2A-rearranged ALL. The EOI remission rate was 93.2%, and the 5-year event-free survival (EFS) for the entire cohort was 69.1% ± 1.9%, with a range from 41.7% ± 17.3% for patients with t(9;11)-positive T-ALL (n = 9) and 64.8% ± 3.0% for patients with t(4;11)-positive B-ALL (n = 266) to 91.2% ± 4.9% for patients with t(11;19)-positive T-ALL (n = 34). Low EOI minimal residual disease was associated with favorable EFS, and induction failure was particularly predictive of nonresponse to further therapy and relapse and poor EFS. In addition, EFS was not improved by allo-HSCT compared with chemotherapy only in patients with both t(4;11)-positive B-ALL (n = 64 v 51; P = .10) and 11q23/KMT2A-rearranged T-ALL (n = 16 v 10; P = .69).

CONCLUSION

Compared with historical data, prognosis of patients with noninfant 11q23/KMT2A-rearranged ALL has improved, but allo-HSCT failed to affect outcome. Targeted therapies are needed to reduce relapse and treatment-related mortality rates.

Measurable residual disease in acute lymphoblastic leukemia: methods and clinical context in adult patients

Measurable residual disease (MRD) is the most powerful independent predictor of risk of relapse and long-term survival in adults and children with acute lymphoblastic leukemia (ALL). For almost all patients with ALL there is a reliable method to evaluate MRD, which can be done using multi-color flow cytometry, quantitative polymerase chain reaction to detect specific fusion transcripts or immunoglobulin/T-cell receptor gene rearrangements, and high-throughput next-generation sequencing. While next-generation sequencing-based MRD detection has been increasingly utilized in clinical practice due to its high sensitivity, the clinical significance of very low MRD levels (<10-4) is not fully characterized. Several new immunotherapy approaches including blinatumomab, inotuzumab ozogamicin, and chimeric antigen receptor T-cell therapies have demonstrated efficacy in eradicating MRD in patients with B-ALL. However, new approaches to target MRD in patients with T-ALL remain an unmet need. As our MRD detection assays become more sensitive and expanding novel therapeutics enter clinical development, the future of ALL therapy will increasingly utilize MRD as a criterion to either intensify or modify therapy to prevent relapse or de-escalate therapy to reduce treatment-related morbidity and mortality.

Circulating Tumor DNA in Pediatric Cancer

The measurement of circulating tumor DNA (ctDNA) has gained increasing prominence as a minimally invasive tool for the detection of cancer-specific markers in plasma. In adult cancers, ctDNA detection has shown value for disease-monitoring applications including tumor mutation profiling, risk stratification, relapse prediction, and treatment response evaluation. To date, there are ctDNA tests used as companion diagnostics for adult cancers and it is not understood why the same cannot be said about childhood cancer, despite the marked differences between adult and pediatric oncology. In this review, we discuss the current understanding of ctDNA as a disease monitoring biomarker in the context of pediatric malignancies, including the challenges associated with ctDNA detection in liquid biopsies. The data and conclusions from pediatric cancer studies of ctDNA are summarized, highlighting treatment response, disease monitoring and the detection of subclonal disease as applications of ctDNA. While the data from retrospective studies highlight the potential of ctDNA, large clinical trials are required for ctDNA analysis for routine clinical use in pediatric cancers. We outline the requirements for the standardization of ctDNA detection in pediatric cancers, including sample handling and reproducibility of results. With better understanding of the advantages and limitations of ctDNA and improved detection methods, ctDNA analysis may become the standard of care for patient monitoring in childhood cancers.

High-throughput sequencing of peripheral blood for minimal residual disease monitoring in childhood precursor B-cell acute lymphoblastic leukemia: A prospective feasibility study

BACKGROUND

Minimal residual disease (MRD) measured on end-of-induction bone marrow (BM) is the most important biomarker for guiding therapy in pediatric acute lymphoblastic leukemia (ALL). Due to limited sensitivity of current approaches, peripheral blood (PB) is not a reliable source for identifying patients needing treatment changes. We sought to determine if high-throughput sequencing (HTS) (next-generation sequencing) of rearranged immunoglobulin and T-cell receptor genes can overcome this and be used to measure MRD in PB.

PROCEDURE

We employed a quantitative HTS approach to accurately measure MRD from one million cell equivalents of DNA from 17 PB samples collected at day 29 after induction therapy in patients with precursor B-cell ALL. We compared these results to the gold-standard real-time PCR result obtained from their paired BM samples, median follow-up 49 months.

RESULTS

With the increased sensitivity, detecting up to one abnormal cell in a million normal cells, we were able to detect MRD in the PB by HTS in all those patients requiring treatment intensification (MRD ≥ 0.005% in BM).

CONCLUSION

This is proof of principle that using the increased sensitivity of HTS, PB can be used to measure MRD and stratify children with ALL. The method is cost effective, rapid, accurate, and reproducible, with inherent advantages in children. Importantly, increasing the frequency testing by PB as opposed to intermittent BM sampling may allow extension of the dynamic range of MRD, giving a more complete picture of the kinetics of disease remission while improving relapse prediction and speed of detection.

The triponderal mass index as a measure of adiposity in pediatric survivors of acute lymphoblastic leukemia: a cross-sectional study

Acute lymphoblastic leukemia (ALL) is the most common type of childhood cancer. Treatments of ALL predispose survivors to obesity, which increases the risk of cardiovascular disease and diabetes. The hallmark of obesity is excess fat mass, and adiposity is a superior predictor of cardiometabolic risk when compared to Body Mass Index (BMI), yet clinical measures of adiposity in children are lacking. The Tri-Ponderal Mass Index (TMI) (kg/m³) is a more accurate adiposity measure compared to BMI z-score in the general pediatric population. This cross-sectional study aimed to validate TMI as an adiposity measure against DEXA scan-derived adiposity, and to compare it to BMI z-score, in pediatric ALL survivors. This study was a retrospective chart review of pediatric ALL survivors diagnosed between 2004 and 2015 at McMaster Children’s Hospital, a tertiary pediatric center in Ontario, Canada. One hundred and thirteen patients (Female n = 55, 48.70%) were included, and adiposity was measured using DEXA scans. Exploratory partial correlations and linear regression analyses were adjusted for age, sex, ethnicity, and ALL risk status. Both TMI and BMI z-score correlated with the DEXA-measured fat mass percentage (FM%) (partial correlation TMI versus FM% r = 0.56; p value < 0.0001; BMI z-score versus FM% r = 0.55; p value < 0.0001). In regression analyses, the association of TMI was not inferior to BMI z-score in assessing adiposity (TMI versus FM% estimated unstandardized B 0.80, 95% CI 0.56, 1.02; p value < 0.0001; BMI z-score versus FM% (unstandardized B 0.37, 95% CI 0.26, 0.49; p value < 0.0001). The TMI is a useful clinical adiposity-specific measure in survivors of pediatric ALL.

Whole-genome sequencing facilitates patient-specific quantitative PCR-based minimal residual disease monitoring in acute lymphoblastic leukaemia, neuroblastoma and Ewing sarcoma

Background

Minimal residual disease (MRD) measurement is a cornerstone of contemporary acute lymphoblastic leukaemia (ALL) treatment. The presence of immunoglobulin (Ig) and T cell receptor (TCR) gene recombinations in leukaemic clones allows widespread use of patient-specific, DNA-based MRD assays. In contrast, paediatric solid tumour MRD remains experimental and has focussed on generic assays targeting tumour-specific messenger RNA, methylated DNA or microRNA.

Methods

We examined the feasibility of using whole-genome sequencing (WGS) data to design tumour-specific polymerase chain reaction (PCR)-based MRD tests (WGS-MRD) in 18 children with high-risk relapsed cancer, including ALL, high-risk neuroblastoma (HR-NB) and Ewing sarcoma (EWS) (n = 6 each).

Results

Sensitive WGS-MRD assays were generated for each patient and allowed quantitation of 1 tumour cell per 10⁻⁴ (0.01%)–10^–5 (0.001%) mononuclear cells. In ALL, WGS-MRD and Ig/TCR-MRD were highly concordant. WGS-MRD assays also showed good concordance between quantitative PCR and droplet digital PCR formats. In serial clinical samples, WGS-MRD correlated with disease course. In solid tumours, WGS-MRD assays were more sensitive than RNA-MRD assays.

Conclusions

WGS facilitated the development of patient-specific MRD tests in ALL, HR-NB and EWS with potential clinical utility in monitoring treatment response. WGS data could be used to design patient-specific MRD assays in a broad range of tumours.

Minimal Residual Disease in Acute Lymphoblastic Leukemia: Current Practice and Future Directions

Simple Summary

Acute lymphoblastic leukemia minimal residual disease (MRD) refers to the presence of residual leukemia cells following the achievement of complete remission, but below the limit of detection using conventional morphologic assessment. Up to two thirds of children may have MRD detectable after induction therapy depending on the biological subtype and method of detection. Patients with detectable MRD have an increased likelihood of relapse. A rapid reduction of MRD reveals leukemia sensitivity to therapy and under this premise, MRD has emerged as the strongest independent predictor of individual patient outcome and is crucial for risk stratification. However, it is a poor surrogate for treatment effect on long term outcome at the trial level, with impending need of randomized trials to prove efficacy of MRD-adapted interventions.

Abstract

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer and advances in its clinical and laboratory biology have grown exponentially over the last few decades. Treatment outcome has improved steadily with over 90% of patients surviving 5 years from initial diagnosis. This success can be attributed in part to the development of a risk stratification approach to identify those subsets of patients with an outstanding outcome that might qualify for a reduction in therapy associated with fewer short and long term side effects. Likewise, recognition of patients with an inferior prognosis allows for augmentation of therapy, which has been shown to improve outcome. Among the clinical and biological variables known to impact prognosis, the kinetics of the reduction in tumor burden during initial therapy has emerged as the most important prognostic variable. Specifically, various methods have been used to detect minimal residual disease (MRD) with flow cytometric and molecular detection of antigen receptor gene rearrangements being the most common. However, many questions remain as to the optimal timing of these assays, their sensitivity, integration with other variables and role in treatment allocation of various ALL subgroups. Importantly, the emergence of next generation sequencing assays is likely to broaden the use of these assays to track disease evolution. This review will discuss the biological basis for utilizing MRD in risk assessment, the technical approaches and limitations of MRD detection and its emerging applications.

How I Diagnose Minimal/Measurable Residual Disease in B Lymphoblastic Leukemia/Lymphoma by Flow Cytometry

OBJECTIVES

Assessment for minimal/measurable residual disease (MRD) is a powerful prognostic factor in B lymphoblastic leukemia/lymphoma (B-LL/L) that is quickly becoming standard of care in assessing patients with B-LL/L posttherapy. MRD can be assessed using methodologies including flow cytometry and molecular genetics, with the former being rapid, relatively inexpensive, and widely applicable in many hematopathology/flow cytometry laboratories.

METHODS

This article presents an approach to MRD detection in B-LL/L by flow cytometry through case presentations with illustration of several potential pitfalls. We review normal maturation patterns, antigens used for assessment, flow panels that can be utilized, considerations to be made during therapy, and clinical impact. The benefits and drawbacks when using the "different from normal" and "leukemia associated phenotype" approaches are considered.

RESULTS

Evaluation for MRD in B-LL/L by flow cytometry relies on a knowledge of normal immunophenotypic patterns associated with B-cell maturation in states of rest and marrow regeneration so that one can identify patterns of antigen expression that differentiate abnormal, leukemic populations from regenerating hematogones or B-cell precursors. The nature of therapy can affect normal patterns, a phenomenon especially important to take into consideration given the increased use of targeted therapies in the treatment of B-LL/L.

CONCLUSIONS

Flow cytometry is widely available in many laboratories and is a cost-effective way to evaluate for B-LL/L MRD. However, panel validation and interpreter education are crucial for accurate assessment.

Monitoring MRD in ALL: Methodologies, technical aspects and optimal time points for measurement

The accurate determination of minimal or measurable residual disease (MRD) during the early months of therapy in acute lymphoblastic leukemia is well established as the most important independent prognostic biomarker, predicting response to combination chemotherapy. Stratification based on MRD maximizes treatment effectiveness while minimizing adverse effects. Allele-specific real-time quantitative PCR of clone-defining immunoglobin/T-cell receptor gene rearrangements in the patients' leukemic clones and/or multiparametric flow cytometric tracking of leukemia-associated immunophenotypes are considered standard of care. Following recent advances in high throughput sequencing (HTS; next generation sequencing), much attention has been devoted to the development of HTS-based MRD assays, which can increase sensitivity; theoretically only limited by the number of cells input into the assay. Knowledge of the methods and limitations of each technology, along with awareness of the sensitivity and specificity of MRD at particular treatment time points is important in interpretation of the MRD value. MRD negativity at pre-established protocol-appropriate time points guides continuance with consolidation/maintenance chemotherapy, whereas positivity leads to a change to a biological therapy such as blinatumomab and intensification of therapy to allogeneic stem cell transplant. Positivity after maintenance may herald impending relapse enabling treatment intervention. MRD has been integral to the introduction of novel agents and cellular therapies into clinical trials and standard of care, but the long-term predictive value of MRD on outcome of novel therapies is not yet established. Integration of somatic genetics with MRD may further improve accurate identification of patients with the lowest and highest risk of relapse.

A review of current induction strategies and emerging prognostic factors in the management of children and adolescents with acute lymphoblastic leukemia

INTRODUCTION

Acute lymphoblastic leukemia is the most frequent hematologic malignancy in children. Almost 95% of children potentially achieve a complete remission after the induction treatment, but over the last years, new insights in the genomic disease profile and in minimal residual disease detection techniques have led to an improvement in the prognostic stratification, identifying selected patients' subgroups with peculiar therapeutic needs.

AREAS COVERED

According to a comprehensive search of peer-review literature performed in Pubmed, in this review we summarize the recent evidences on the induction treatment strategies comprised in the children acute lymphoblastic leukemia scenario, focusing on the role of key drugs such as corticosteroids and asparaginase and discussing the crucial significance of the genomic characterization at baseline which may drive the proper induction treatment choice.

EXPERT OPINION

Current induction strategies already produce durable remissions in a significant proportion of standard-risk children with acute lymphoblastic leukemia. A broader knowledge of the biologic features related to acute lymphoblastic leukemia subtypes with worse prognosis, and an optimization of targeted drugs now available, might lead to the achievement of long-term molecular remissions in this setting.

Outcome in Children With Standard-Risk B-Cell Acute Lymphoblastic Leukemia: Results of Children's Oncology Group Trial AALL0331

PURPOSE

Children's Oncology Group (COG) AALL0331 tested whether intensified postinduction therapy that improves survival in children with high-risk B-cell acute lymphoblastic leukemia (ALL) would also improve outcomes for those with standard-risk (SR) ALL.

PATIENTS AND METHODS

AALL0331 enrolled 5,377 patients between 2005 and 2010. All patients received a 3-drug induction with dexamethasone, vincristine, and pegaspargase (PEG) and were then classified as SR low, SR average, or SR high. Patients with SR-average disease were randomly assigned to receive either standard 4-week consolidation (SC) or 8-week intensified augmented Berlin-Frankfurt-Münster (BFM) consolidation (IC). Those with SR-high disease were nonrandomly assigned to the full COG-augmented BFM regimen, including 2 interim maintenance and delayed intensification phases.

RESULTS

The 6-year event-free survival (EFS) rate for all patients enrolled in AALL0331 was 88.96% ± 0.46%, and overall survival (OS) was 95.54% ± 0.31%. For patients with SR-average disease, the 6-year continuous complete remission (CCR) and OS rates for SC versus IC were 87.8% ± 1.3% versus 89.1% ± 1.2% (P = .52) and 95.8% ± 0.8% versus 95.2% ± 0.8% (P = 1.0), respectively. Those with SR-average disease with end-induction minimal residual disease (MRD) of 0.01% to < 0.1% had an inferior outcome compared with those with lower MRD and no improvement with IC (6-year CCR: SC, 77.5% ± 4.8%; IC, 77.1% ± 4.8%; P = .71). At 6 years, the CCR and OS rates among 635 nonrandomly treated patients with SR-high disease were 85.55% ± 1.49% and 92.97% ± 1.08%, respectively.

CONCLUSION

The 6-year OS rate for > 5,000 children with SR ALL enrolled in AALL0331 exceeded 95%. The addition of IC to treatment for patients with SR-average disease did not improve CCR or OS, even in patients with higher MRD, in whom it might have been predicted to provide more value. The EFS and OS rates are excellent for this group of patients with SR ALL, with particularly good outcomes for those with SR-high disease.

Impact of dose and duration of therapy on dexamethasone pharmacokinetics in childhood acute lymphoblastic leukaemia-a report from the UKALL 2011 trial

INTRODUCTION

The use of dexamethasone in acute lymphoblastic leukaemia therapy contributes to short- and long-term toxicities. The UKALL 2011 randomised trial investigated whether a more intense dexamethasone dose (10 mg/m2/d x 14d, short vs 6 mg/m2/d x 28d, standard) would lead to a more rapid cytoreduction and reduced adverse effects associated with longer durations of steroids in induction. The impact of dose and duration on dexamethasone pharmacokinetics was investigated.

METHODS

Blood samples were obtained on one of the first three and last three days of induction dexamethasone dosing at time points up to 8 h after oral administration. Plasma dexamethasone levels were quantified in 1084 plasma samples obtained from 174 children and a population pharmacokinetic model developed.

RESULTS

Drug exposure varied significantly between patients, with a >12-fold variation in AUC0-12h values and a marked overlap in dexamethasone exposures between dose levels. Intuitively, AUC0-12h was significantly higher with short dosing (10 mg/m2/d), but cumulative exposure was significantly higher with standard dosing over 28 days, after a higher cumulative dose. Concomitant rasburicase administration was associated with a 60% higher dexamethasone clearance. Day 8 bone marrow response was comparable between dosing arms, but those with <5% blast count exhibited a greater mean dexamethasone exposure than those with >5%. No statistical differences were observed between arms in terms of steroid-related toxicity or minimal residual disease at the end of induction.

CONCLUSION

The potential significance of dexamethasone AUC0-12h on early response and higher cumulative exposure on the standard arm suggest that duration of therapy and exposure may be more important factors than absolute dose from a clinical pharmacology perspective.

[Clinical application of minimal residual disease detection in childhood acute leukemia]

In recent years, great progress has been made in the treatment outcome of childhood acute leukemia with the improvement of chemotherapy regimens and the introduction of risk-stratified therapy; however, minimal residual disease (MRD) is still a difficult problem which affects the prognosis of acute leukemia. MRD influences the selection of chemotherapy regimens and recurrence risk stratification, and meanwhile, it can be used for prognostic prediction. At present, flow cytometry and polymerase chain reaction are mainly used for MRD detection. The next-generation sequencing also plays an important role in MRD detection, especially in MRD detection after stem cell transplantation. This article reviews the methodology and significance of MRD detection in childhood acute leukemia.

Childhood cancer incidence and survival in Japan and England: A population-based study (1993-2010)

The present study aimed to compare cancer incidence and trends in survival for children diagnosed in Japan and England, using population-based cancer registry data. The analysis was based on 5192 children with cancer (age 0-14 years) from 6 prefectural cancer registries in Japan and 21 295 children diagnosed in England during 1993-2010. Differences in incidence rates between the 2 countries were measured with Poisson regression models. Overall survival was estimated using the Kaplan-Meier method. Incidence rates for Hodgkin lymphoma, renal tumors and Ewing sarcomas in England were more than twice as high as those in Japan. Incidence of germ cell tumors, hepatic tumors, neuroblastoma and acute myeloid leukemia (AML) was higher in Japan than in England. Incidence of all cancers combined decreased in Japan throughout the period 1993 to 2010, which was mainly explained by a decrease in registration of neuroblastoma in infants. For many cancers, 5-year survival improved in both countries. The improvement in survival in chronic myeloid leukemia (CML) was particularly dramatic in both countries. However, 5-year survival remained less than 80% in 2005-2008 in both countries for AML, brain tumors, soft tissue sarcomas, malignant bone tumors and neuroblastoma (age 1-14 years). There were significant differences in incidence of several cancers between countries, suggesting variation in genetic susceptibility and possibly environmental factors. The decrease in incidence for all cancers combined in Japan was related to the cessation of the national screening program for neuroblastoma. The large improvement in survival in CML coincided with the introduction of effective therapy (imatinib).

Genotype-Specific Minimal Residual Disease Interpretation Improves Stratification in Pediatric Acute Lymphoblastic Leukemia

Purpose Minimal residual disease (MRD) and genetic abnormalities are important risk factors for outcome in acute lymphoblastic leukemia. Current risk algorithms dichotomize MRD data and do not assimilate genetics when assigning MRD risk, which reduces predictive accuracy. The aim of our study was to exploit the full power of MRD by examining it as a continuous variable and to integrate it with genetics. Patients and Methods We used a population-based cohort of 3,113 patients who were treated in UKALL2003, with a median follow-up of 7 years. MRD was evaluated by polymerase chain reaction analysis of Ig/TCR gene rearrangements, and patients were assigned to a genetic subtype on the basis of immunophenotype, cytogenetics, and fluorescence in situ hybridization. To examine response kinetics at the end of induction, we log-transformed the absolute MRD value and examined its distribution across subgroups. Results MRD was log normally distributed at the end of induction. MRD distributions of patients with distinct genetic subtypes were different ( P < .001). Patients with good-risk cytogenetics demonstrated the fastest disease clearance, whereas patients with high-risk genetics and T-cell acute lymphoblastic leukemia responded more slowly. The risk of relapse was correlated with MRD kinetics, and each log reduction in disease level reduced the risk by 20% (hazard ratio, 0.80; 95% CI, 0.77 to 0.83; P < .001). Although the risk of relapse was directly proportional to the MRD level within each genetic risk group, absolute relapse rate that was associated with a specific MRD value or category varied significantly by genetic subtype. Integration of genetic subtype-specific MRD values allowed more refined risk group stratification. Conclusion A single threshold for assigning patients to an MRD risk group does not reflect the response kinetics of the different genetic subtypes. Future risk algorithms should integrate genetics with MRD to accurately identify patients with the lowest and highest risk of relapse.

Clinical impact of minimal residual disease in children with different subtypes of acute lymphoblastic leukemia treated with Response-Adapted therapy

To determine the clinical significance of minimal residual disease (MRD) in patients with prognostically relevant subtypes of childhood acute lymphoblastic leukemia (ALL), we analyzed data from 488 patients treated in St Jude Total Therapy Study XV with treatment intensity based mainly on MRD levels measured during remission induction. MRD levels on day 19 predicted treatment outcome for patients with hyperdiploid >50 ALL, National Cancer Institute (NCI) standard-risk B-ALL or T-cell ALL, while MRD levels on day 46 were prognostic for patients with NCI standard-risk or high-risk B-ALL. Patients with t(12;21)/(ETV6-RUNX1) or hyperdiploidy >50 ALL had the best prognosis; those with a negative MRD on day 19 had a particularly low risk of relapse: 1.9% and 3.8%, respectively. Patients with NCI high-risk B-ALL or T-cell ALL had an inferior outcome; even with undetectable MRD on day 46, cumulative risk of relapse was 12.7% and 15.5%, respectively. Among patients with NCI standard-risk B-ALL, the outcome was intermediate overall but was poor if MRD was ⩾1% on day 19 or MRD was detectable at any level on day 46. Our results indicate that the clinical impact of MRD on treatment outcome in childhood ALL varies considerably according to leukemia subtype and time of measurement.