Reduced-intensity therapy for pediatric lymphoblastic leukemia: impact of residual disease early in remission induction

Measurable residual disease (MRD)-testing in haematological cancers: A giant leap forward or sideways?

Measurable residual disease (MRD)-testing is used in many haematological cancers to estimate relapse risk and to direct therapy. Sometimes MRD-test results are used for regulatory approval. However, some people including regulators wrongfully believe results of MRD-testing are highly accurate and of proven efficacy in directing therapy. We review MRD-testing technologies and evaluate the accuracy of MRD-testing for predicting relapse and the strength of evidence supporting efficacy of MRD-guided therapy. We show that at the individual level MRD-test results are often an inaccurate relapse predictor. Also, no convincing data indicate that increasing therapy-intensity based on a positive MRD-test reduces relapse risk or improves survival. We caution against adjusting therapy-intensity based solely on results of MRD-testing.

Diagnostic and treatment strategies for pediatric acute lymphoblastic leukemia in low- and middle-income countries

The survival rate of children and adolescents with acute lymphoblastic leukemia (ALL), the most common pediatric cancer, has improved significantly in high-income countries (HICs), serving as an excellent example of how humans can overcome catastrophic diseases. However, the outcomes in children with ALL in low- and middle-income countries (LMICs), where approximately 80% of the global population live, are suboptimal because of limited access to diagnostic procedures, chemotherapeutic agents, supportive care, and financial assistance. Although the implementation of therapeutic strategies in resource-limited countries could theoretically follow the same path of improvement as modeled in HICs, intensification of chemotherapy may simply result in increased toxicities. With the advent of genetic diagnosis, molecular targeted therapy, and immunotherapy, the management of ALL is changing dramatically in HICs. Multidisciplinary collaborations between institutions in LMICs and HICs will provide access to strategies that are suitable for institutions in LMICs, enabling them to minimize toxicities while improving outcomes. This article summarizes important aspects of the diagnosis and treatment of pediatric ALL that were mostly developed in HICs but that can be realistically implemented by institutions in countries with limited resources through resource-adapted multidisciplinary collaborations.

Flow cytometric minimal residual disease measurement accounting for cytogenetics in children with non-high-risk acute lymphoblastic leukemia treated according to the ALL-MB 2008 protocol

BACKGROUND

Quantitative measurement of minimal residual disease (MRD) is the "gold standard" for estimating the response to therapy in childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Nevertheless, the speed of the MRD response differs for different cytogenetic subgroups. Here we present results of MRD measurement in children with BCP-ALL, in terms of genetic subgroups with relation to clinically defined risk groups.

METHODS

A total of 485 children with non-high-risk BCP-ALL with available cytogenetic data and MRD studied at the end-of-induction (EOI) by multicolor flow cytometry (MFC) were included. All patients were treated with standard-risk (SR) of intermediate-risk (ImR) regimens of "ALL-MB 2008" reduced-intensity protocol.

RESULTS AND DISCUSSION

Among all study group patients, 203 were found to have low-risk cytogenetics (ETV6::RUNX1 or high hyperdiploidy), while remaining 282 children were classified in intermediate cytogenetic risk group. For the patients with favorable and intermediate risk cytogenetics, the most significant thresholds for MFC-MRD values were different: 0.03% and 0.04% respectively. Nevertheless, the most meaningful thresholds were different for clinically defined SR and ImR groups. For the SR group, irrespective to presence/absence of favorable genetic lesions, MFC-MRD threshold of 0.1% was the most clinically valuable, although for ImR group the most informative thresholds were different in patients from low-(0.03%) and intermediate (0.01%) cytogenetic risk groups.

CONCLUSION

Our data show that combining clinical risk factors with MFC-MRD measurement is the most useful tool for risk group stratification of children with BCP-ALL in the reduced-intensity protocols. However, this algorithm can be supplemented with cytogenetic data for part of the ImR group.

Childhood acute lymphoblastic leukemia: Four years evaluation of protocols 2013 and 2016 in a single center in Indonesia, a lower-middle-income country

BACKGROUND

The prognosis of childhood acute lymphoblastic leukemia (ALL) in Indonesia, a lower-middle-income country (LMIC), is lower than in high income countries (HICs). The Indonesian ALL2013 protocol resulted in too many toxic deaths (21%) and abandonments (11%). Therefore, we drafted an adapted protocol, ALL2016. Main changes: no anthracyclines in standard risk (SR), prednisone replaced dexamethasone at induction in high risk (HR), and anthracyclines and cyclophosphamide were rescheduled in HR.

PROCEDURE

Patients (aged: 1-18 years) were stratified into SR and HR. HR was defined as age over 10 years, leucocyte count over 50 × 10⁹ /L, central nervous system (CNS) involvement, mediastinal mass, T-cell phenotype, testicular involvement, or poor prednisone response.

RESULTS

ALL2013 included 174 patients (106 SR and 68 HR) and ALL2016 188 (91 SR and 97 HR). Although the number of HR patients was significantly higher in ALL2016 (51.6% vs. 39.1%; p = .017), the outcome of ALL2016 improved over ALL2013 (4-year-probable overall survival (pOS) 60.1% vs. 50.0%; p = .042 and 4-year-probable event-free survival (pEFS) 49.5% vs. 36.8%; p = .018). ALL2016 showed a nonsignificant advantage for SR patients (4-year-pEFS 56.0% vs. 47.2%; p = .220 and 4-year-pOS 70.3% vs. 61.3%; p = .166), but less toxic deaths (7% vs. 20%; p = .011). In HR group, the outcomes were significantly better in ALL2016 (4-year-pEFS 43.3% vs. 20.6%; p = .004; 4-year-pOS 50.5% vs. 32.4%; p = .014) especially due to less relapses (31% vs. 62%; p = .001). Isolated CNS relapses went down from 18 to 8% in HR (p = .010) and 11 to 5% in SR (p = .474). Both SR and HR showed lower numbers of abandonment in ALL2016 (6% vs. 14%; p = .039).

CONCLUSIONS

Overall ALL2016 results improved over ALL2013. Modest changes in protocol resulted in less initial toxicity and abandonments.

One-point flow cytometric MRD measurement to identify children with excellent outcome after intermediate-risk BCP-ALL: results of the ALL-MB 2008 study

BACKGROUND

 Measurement of minimal residual disease (MRD) with multicolor flow cytometry (MFC) has become an important tool in childhood acute lymphoblastic leukemia (ALL), mainly to identify rapid responders and reduce their therapy intensity. Protocols of the Moscow-Berlin (MB) group use a comparatively low (for standard risk; SR) or moderate (for intermediate risk; ImR) treatment intensity from the onset, based on initial patient characteristics. Recently, we reported that 90% of SR patients-50% B cell precursor (BCP-ALL)-MFC-MRD negative at end of induction (EOI)-had 95% event-free survival (EFS).  METHODS: In the present study, we applied this method to children with initial ImR features.

RESULTS

 In study MB 2008, 1105 children-32% of BCP-ALL patients-were assigned to the ImR group. Of these, 227 were treated in clinics affiliated with MFC laboratories of the MB group network, and included in this MFC-MRD pilot study. A single-point MFC-MRD measurement at the EOI with the threshold of 0.01% identified 65% of patients-20% of all BCP-ALL patients-with EFS of 93.5%.

CONCLUSION

 Taking both studies together, the combination of clinical parameters and a one-point MRD measurement identifies 70% of BCP-ALL patients with an excellent outcome after low- or moderate-intensity therapy and avoids overtreatment of a significant proportion of patients.

Digital PCR for Minimal Residual Disease Quantitation Using Immunoglobulin/T-Cell Receptor Gene Rearrangements in Acute Lymphoblastic Leukemia: A Proposed Analytic Algorithm

In minimal residual disease (MRD), where there are exceedingly low target copy numbers, digital PCR (dPCR) can improve MRD quantitation. However, standards for dPCR MRD interpretation in acute lymphoblastic leukemia are lacking. Here, for immunoglobulin/T-cell receptor-based MRD, we propose an objective, statistics-based analytic algorithm. In 161 postinduction samples from 79 children with acute lymphoblastic leukemia, MRD was performed by dPCR and real-time quantitative PCR (qPCR) using the same markers and primer-probe sets. The dPCR raw data were analyzed by using an automated algorithm. dPCR and qPCR results were highly concordant (P < 0.0001): 98% (50 of 51) of qPCR positive were positive by dPCR, whereas 95% (61 of 64) of qPCR negative results were also negative by dPCR. For MRD quantitation, both qPCR and dPCR were tightly correlated (R² = 0.94). Using more DNA (1 μg × 7 versus 630 ng × 3), dPCR improved sensitivity of MRD quantitation by one log₁₀ (median MRD positive cutoff 1.6 × 10^-5). With dPCR, 83% (29 of 35) of positive-not-quantifiable results by qPCR could be assigned positive/negative MRD status. Seven replicates of tested samples and negative controls were optimal. Compared with qPCR, dPCR could improve MRD sensitivity by one log₁₀. We proposed an automatable, statistics-based algorithm that minimized interoperator variance for dPCR MRD.

Precursor B-cell acute lymphoblastic leukaemia-a global view

As haematologists, we always seek to follow standardised guidelines for practice and apply the best treatment within our means for our patients with blood diseases. However, treatment can never follow an exact recipe. Opinions differ as to the best approach; sometimes more than one treatment approach results in identical outcomes, or treatments differ only by the manner in which they fail. Furthermore, the haematologist is faced with constraints relating to the local economic environment. Patients too are not the same the world over. Early presentation is commoner in the developed world, as is the patient’s understanding of the disease process. This in turn has an impact on the way patients are managed, the rigorousness of patient adhesion to the treatment schedule and the outcome. Here we take a look at the precursor B‐cell acute lymphoblastic leukaemia in an adolescent in a range of different settings from low‐ to high income countries with widely differing challenges for diagnosis, therpy and follow‐up. For these reasons, given the same starting conditions, patients will be treated differently according to the institute and the country they are in. Experts from around the world have been tasked to describe their management plan and rationale for a specific disease presentation. Here they explore the management of precursor B‐cell acute lymphoblastic leukaemia (pre‐B ALL) in five different institutions worldwide with a focus on those with more or less strained economies. We end with a conclusion from an expert in the field comparing and contrasting these different management styles and considering their merits and limitations.

Curing the Curable: Managing Low-Risk Acute Lymphoblastic Leukemia in Resource Limited Countries

Although childhood acute lymphoblastic leukemia (ALL) is curable, global disparities in treatment outcomes remain. To reduce these global disparities in low-middle income countries (LMIC), a paradigm shift is needed: start with curing low-risk ALL. Low-risk ALL, which accounts for >50% of patients, can be cured with low-toxicity therapies already defined by collaborative studies. We reviewed the components of these low-toxicity regimens in recent clinical trials for low-risk ALL and suggest how they can be adopted in LMIC. In treating childhood ALL, the key is risk stratification, which can be resource stratified. NCI standard-risk criteria (age 1–10 years, WBC < 50,000/uL) is simple yet highly effective. Other favorable features such as ETV6-RUNX1, hyperdiploidy, early peripheral blood and bone marrow responses, and simplified flow MRD at the end of induction can be added depending on resources. With limited supportive care in LMIC, more critical than relapse is treatment-related morbidity and mortality. Less intensive induction allows early marrow recovery, reducing the need for intensive supportive care. Other key elements in low-toxicity protocol designs include: induction steroid type; high-dose versus low-dose escalating methotrexate; judicious use of anthracyclines; and steroid pulses during maintenance. In summary, the first effective step in curing ALL in LMIC is to focus on curing low-risk ALL with less intensive therapy and less toxicity.

Treatment of children with acute lymphoblastic leukemia in Cambodia

We report a retrospective analysis of 110 unselected pediatric patients with acute lymphoblastic leukemia (ALL) treated during 2015-2017 in a charity-funded public institution in Cambodia with a reduced intensity ALL-Moscow Berlin (MB)-91 protocol. No patient abandoned treatment. Sixty-three patients (57%) were high risk (HR). Seventy-two patients (65.5%) reached complete remission (CR) on day 36. The 3-year event-free survival (EFS) and overall survival (OS) was 34.9% (50.5% for standard risk [SR]). Most deaths resulted from infections (40 [53.3%]) and bleeding (15 [20%]). With further selective reduction of treatment intensity and access to platelet infusion, leukemia therapy is justified in this setting.

Utilizing the prognostic impact of minimal residual disease in treatment decisions for pediatric acute lymphoblastic leukemia

INTRODUCTION

Acute lymphoblastic leukemia (ALL) is the first pediatric cancer where the assessment of early response to therapy by minimal residual disease (MRD) monitoring has demonstrated its importance to improve risk-based treatment approaches. The most standardized tools to study MRD in ALL are multiparametric flow cytometry and realtime-quantitative polymerase chain reaction amplification-based methods. In recent years, MRD measurement has reached greater levels of sensitivity and standardization through international laboratory networks collaboration.

AREAS COVERED

We herewith describe how to assess and apply the prognostic impact of MRD in treatment decisions, with specific focus on pediatric ALL. We also highlight the role of MRD monitoring in the context of genetically homogeneous subgroups of pediatric ALL. However, some queries remain to be addressed and emerging technologies hold the promise of improving MRD detection in ALL patients.

EXPERT OPINION

Emerging technologies, like next generation flow cytometry, droplet digital PCR, and next generation sequencing appear to be important methods for assessing MRD in pediatric ALL. These more specific and/or sensitive MRD monitoring methods may help to predict relapse with greater accuracy, and are currently being used in clinical trials to improve pediatric ALL outcome by optimizing patient stratification and earlier MRD-based interventional therapy.

A Hopeful Leap Forward by Multicentric Cooperation for Precision-Based Therapy for Very Resistant, Relapsed, or Refractory Childhood Leukemia

Pikman and colleagues report the results of a multicentric prospective clinical trial of the leukemia precision-based therapy (LEAP) consortium that combines identification of targetable lesions in drug-resistant childhood leukemia, tiered based on evidence for genomic lesions and drug target, validation of matching small-molecule targeted agents, and treatment of individual patients. The study demonstrates the impact of genomic information on disease classification, treatment guidance, and translational research, but also illustrates the challenges for target prediction and trial design for increasingly heterogeneous and smaller subgroups of patients.See related article by Pikman et al., p. 1424.