International cooperative study identifies treatment strategy in childhood ambiguous lineage leukemia

Case report: Venetoclax plus Azacitidine in treatment of acute undifferentiated leukemia

OBJECTIVES

Acute undifferentiated leukemia (AUL) is a clinical rare leukemia with an overall poor prognosis. Currently, there are no well-established treatment guidelines for AUL, further exploration of optimal treatment options is now required.

METHODS

We report an AUL patient who was complicated by a NRAS mutation and del5q was admitted to our hospital and we present the clinical features. In addition, we conducted a literature review.

RESULTS

The "VA" scheme combines agents Venetoclax and Azacitidine that have synergistic therapeutic effect with a tolerable safety profile. There is no previous report of the "VA" scheme employed in AUL treatment. An AUL patient who was complicated by a NRAS mutation and del5q was admitted to our hospital. The "VA" scheme was administrated, and complete remission (CR) was achieved at the end of the first cycle. The patient then underwent HLA-identical sibling allogeneic hematopoietic stem cell transplantation.

DISCUSSION

The "VA" scheme has been extensively used in AML treatment, but its application in AUL treatment has not yet been reported. This study is the first to report an AUL patient treated with the "VA" scheme and achieved CR. Our result preliminarily suggested the effectiveness and safety of the "VA" scheme in AUL treatment, but validation is required in more clinical samples. The "VA" scheme provides a new treatment option for AUL patients and deserves further clinical promotion.

Multiomic single cell sequencing identifies stemlike nature of mixed phenotype acute leukemia

Despite recent work linking mixed phenotype acute leukemia (MPAL) to certain genetic lesions, specific driver mutations remain undefined for a significant proportion of patients and no genetic subtype is predictive of clinical outcomes. Moreover, therapeutic strategy for MPAL remains unclear, and prognosis is overall poor. We performed multiomic single cell profiling of 14 newly diagnosed adult MPAL patients to characterize the inter- and intra-tumoral transcriptional, immunophenotypic, and genetic landscapes of MPAL. We show that neither genetic profile nor transcriptome reliably correlate with specific MPAL immunophenotypes. Despite this, we find that MPAL blasts express a shared stem cell-like transcriptional profile indicative of high differentiation potential. Patients with the highest differentiation potential demonstrate inferior survival in our dataset. A gene set score, MPAL95, derived from genes highly enriched in the most stem-like MPAL cells, is applicable to bulk RNA sequencing data and is predictive of survival in an independent patient cohort, suggesting a potential strategy for clinical risk stratification.

Case report: An intriguing case of Philadelphia chromosome-positive acute lymphoblastic leukemia recurrence

The incorporation of tyrosine kinase inhibitors (TKIs) in the treatment of Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) led to significant improvement. However, in the pediatric setting, the outcomes of Ph+ ALL are still inferior compared to those of other ALL subtypes even in the TKI era due to higher relapse rate. Herein, we report a very peculiar case of late extramedullary Ph+ ALL relapse in a child, characterized by lymphomatous presentation in the tonsils and lymphoid lineage switch. The diagnostic dilemma between the occurrence of a second malignant neoplasm and the recurrence of the primary disease is further discussed, highlighting the importance of molecular backtracking analysis. This case report emphasizes the high plasticity and polyclonal nature of ALL and expands the heterogeneity of possible clinical presentation of Ph+ ALL at relapse.

Clinical features of immature leukemias in children

Early T-cell precursor acute lymphoblastic leukemia (ETP-ALL), mixed phenotypic acute leukemia (MPAL), and acute myeloid leukemia with minimal differentiation (AML-M0) all originate from immature hematopoietic progenitor cells and have a poor prognosis. We investigated the clinical characteristics of these immature leukemias in 17 children (ETP-ALL: 8, MPAL: 5, AML-M0: 4) at seven institutions. Clinical and laboratory findings were comparable across disease types. Eleven and six patients received ALL- and AML-oriented induction chemotherapy, with six and four achieving complete remission (CR), respectively. Five additional patients achieved CR after salvage with the other type of chemotherapy. Eight patients received hematopoietic cell transplantation (HCT) in first CR, and six survived without relapse. However, six of seven patients who did not receive HCT during first CR relapsed; all underwent HCT later, and only three survived. The 5-year event-free survival (EFS) and overall survival (OS) rate were 37% and 69%, respectively. Patients who achieved CR after induction chemotherapy and received HCT in first CR had favorable EFS and OS. Notably, all patients who received HCT in first CR survived 5 years after diagnosis. Appropriate induction chemotherapy and HCT in first CR could improve the outcome of immature leukemias.

Acute leukemia with KMT2A rearrangement: A master of disguise

Mixed-phenotype acute leukemia (MPAL) is a rare form of leukemia with ambiguous lineage, and there are challenges in accurately diagnosing this entity according to formal criteria. Here we report a case which was initially diagnosed as "AML" based on atypical peripheral blood flow cytometry that was subsequently determined to be B-ALL with KMT2A rearrangement based on marrow results. Although KMT2A rearrangements represent a defining genetic abnormality for acute leukemia of ambiguous lineage, this case did not meet the criteria for MPAL based on WHO 2022 criteria. This case highlights the diagnostic challenges of MPAL and the potential limitations of the current classification. We discuss the most appropriate workup and management of these patients and identify areas for future study.

A hybrid protocol CLAG-M, a possible player for the first-line therapy of patients with mixed phenotype acute leukemia. A Polish Adult Leukemia Group experience

Introduction

Mixed-phenotype acute leukemia (MPAL) is a rare disease with poor prognosis. So far, no standard approach has been established as the "know-how" of MPAL is based only on retrospective analyses performed on small groups of patients.

Materials and methods

In this study, a retrospective analysis of the outcomes of adult MPAL patients included in the PALG registry between 2005 and 2024 who received the CLAG-M hybrid protocol as induction or salvage therapy was performed.

Results

Sixteen of 98 MPAL patients received CLAG-M: eight as first-line and eight as salvage therapy. In the first line, two patients achieved partial response (PR), and six achieved complete remission (CR), of whom four successfully underwent allogeneic hematopoietic stem cell transplantation (alloHSCT). Two patients who did not undergo alloHSCT promptly relapsed. Within the whole group, the overall response rate (ORR) was 75% (n = 12/16). With the median follow-up of 13 months, six out of eight patients remain in CR, however, two of them died due to acute graft versus host disease. Out of eight patients who received CLAG-M in the second line, four patients (50%) obtained CR. AlloHSCT was conducted in seven cases, six of which were in CR. Only two patients remained in CR at the time of the last follow-up. Tolerance to treatment was good. The median times for severe neutropenia and thrombocytopenia were 22 days (range, 16-24) and 17 days (range, 12-24), respectively. Overall, grade 3-4 infections were observed in 12 cases, and all infections presented successful outcomes.

Conclusions

CLAG-M is an effective first-line salvage regimen for MPAL with an acceptable safety profile. Early achievement of CR with prompt alloHSCT allows for satisfactory disease control.

CD371-positive pediatric B-cell acute lymphoblastic leukemia: propensity to lineage switch and slow early response to treatment

ABSTRACT

In the effort to improve immunophenotyping and minimal residual disease (MRD) assessment in acute lymphoblastic leukemia (ALL), the international Berlin-Frankfurt-Münster (iBFM) Flow Network introduced the myelomonocytic marker CD371 for a large prospective characterization with a long follow-up. In the present study, we aimed to investigate the clinical and biological features of CD371-positive (CD371pos) pediatric B-cell precursor ALL (BCP-ALL). From June 2014 to February 2017, 1812 pediatric patients with newly diagnosed BCP-ALLs enrolled in trial AIEOP-BFM ALL 2009 were evaluated as part of either a screening (n = 843, Italian centers) or validation cohort (n = 969, other iBFM centers). Laboratory assessment at diagnosis consisted of morphological, immunophenotypic, and genetic analysis. Response assessment relied on morphology, multiparametric flow cytometry (MFC), and polymerase chain reaction (PCR)-MRD. At diagnosis, 160 of 1812 (8.8%) BCP-ALLs were CD371pos. This correlated with older age, lower ETV6::RUNX1 frequency, immunophenotypic immaturity (all P < .001), and strong expression of CD34 and of CD45 (P < .05). During induction therapy, CD371pos BCP-ALLs showed a transient myelomonocytic switch (mm-SW: up to 65.4% of samples at day 15) and an inferior response to chemotherapy (slow early response, P < .001). However, the 5-year event-free survival was 88.3%. Among 420 patients from the validation cohort, 27 of 28 (96.4%) cases positive for DUX4-fusions were CD371pos. In conclusion, in the largest pediatric cohort, CD371 is the most sensitive marker of transient mm-SW, whose recognition is essential for proper MFC MRD assessment. CD371pos is associated to poor early treatment response, although a good outcome can be reached after MRD-based ALL-related therapies.

Biological Markers of High-Risk Childhood Acute Lymphoblastic Leukemia

Childhood acute lymphoblastic leukemia (ALL) has witnessed substantial improvements in prognosis; however, a subset of patients classified as high-risk continues to face higher rates of relapse and increased mortality. While the National Cancer Institute (NCI) criteria have traditionally guided risk stratification based on initial clinical information, recent advances highlight the pivotal role of biological markers in shaping the prognosis of childhood ALL. This review delves into the emerging understanding of high-risk childhood ALL, focusing on molecular, cytogenetic, and immunophenotypic markers. These markers not only contribute to unraveling the underlying mechanisms of the disease, but also shed light on specific clinical patterns that dictate prognosis. The paradigm shift in treatment strategies, exemplified by the success of tyrosine kinase inhibitors in Philadelphia chromosome-positive leukemia, underscores the importance of recognizing and targeting precise risk factors. Through a comprehensive exploration of high-risk childhood ALL characteristics, this review aims to enhance our comprehension of the disease, offering insights into its molecular landscape and clinical intricacies in the hope of contributing to future targeted and tailored therapies.

Acute myeloid leukemia with mixed phenotype is characterized by stemness transcriptomic signatures and limited lineage plasticity

Mixed phenotype (MP) in acute leukemias poses unique classification and management dilemmas and can be seen in entities other than de novo mixed phenotype acute leukemia (MPAL). Although WHO classification empirically recommends excluding AML with myelodysplasia related changes (AML-MRC) and therapy related AML (t-AML) with mixed phenotype (AML-MP) from MPAL, there is lack of studies investigating the clinical, genetic, and biologic features of AML-MP. We report the first cohort of AML-MRC and t-AML with MP integrating their clinical, immunophenotypic, genomic and transcriptomic features with comparison to MPAL and AML-MRC/t-AML without MP. Both AML cohorts with and without MP shared similar clinical features including adverse outcomes but were different from MPAL. The genomic landscape of AML-MP overlaps with AML without MP but differs from MPAL. AML-MP harbors more frequent RUNX1 mutations than AML without MP and MPAL. RUNX1 mutations did not impact the survival of patients with MPAL. Unsupervised hierarchal clustering based on immunophenotype identified biologically distinct clusters with phenotype/genotype correlation and outcome differences. Furthermore, transcriptomic analysis showed an enrichment for stemness signature in AML-MP and AML without MP as compared to MPAL. Lastly, MPAL but not AML-MP often switched to lymphoid only immunophenotype after treatment. Expression of transcription factors critical for lymphoid differentiation were upregulated only in MPAL, but not in AML-MP. Our study for the first time demonstrates that AML-MP clinically and biologically resembles its AML counterpart without MP and differs from MPAL, supporting the recommendation to exclude these patients from the diagnosis of MPAL. Future studies are needed to elucidate the molecular mechanism of mixed phenotype in AML.

Key points

AML-MP clinically and biologically resembles AML but differs from MPAL. AML-MP shows RUNX1 mutations, stemness signatures and limited lymphoid lineage plasticity.

Single-cell RNA sequencing distinctly characterizes the wide heterogeneity in pediatric mixed phenotype acute leukemia

BACKGROUND

Mixed phenotype acute leukemia (MPAL), a rare subgroup of leukemia characterized by blast cells with myeloid and lymphoid lineage features, is difficult to diagnose and treat. A better characterization of MPAL is essential to understand the subtype heterogeneity and how it compares with acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). Therefore, we performed single-cell RNA sequencing (scRNAseq) on pediatric MPAL bone marrow (BM) samples to develop a granular map of the MPAL blasts and microenvironment landscape.

METHODS

We analyzed over 40,000 cells from nine pediatric MPAL BM samples to generate a single-cell transcriptomic landscape of B/myeloid (B/My) and T/myeloid (T/My) MPAL. Cells were clustered using unsupervised single-cell methods, and malignant blast and immune clusters were annotated. Differential expression analysis was performed to identify B/My and T/My MPAL blast-specific signatures by comparing transcriptome profiles of MPAL with normal BM, AML, and ALL. Gene set enrichment analysis (GSEA) was performed, and significantly enriched pathways were compared in MPAL subtypes.

RESULTS

B/My and T/My MPAL blasts displayed distinct blast signatures. Transcriptomic analysis revealed that B/My MPAL profile overlaps with B-ALL and AML samples. Similarly, T/My MPAL exhibited overlap with T-ALL and AML samples. Genes overexpressed in both MPAL subtypes' blast cells compared to AML, ALL, and healthy BM included MAP2K2 and CD81. Subtype-specific genes included HBEGF for B/My and PTEN for T/My. These marker sets segregated bulk RNA-seq AML, ALL, and MPAL samples based on expression profiles. Analysis comparing T/My MPAL to ETP, near-ETP, and non-ETP T-ALL, showed that T/My MPAL had greater overlap with ETP-ALL cases. Comparisons among MPAL subtypes between adult and pediatric samples showed analogous transcriptomic landscapes of corresponding subtypes. Transcriptomic differences were observed in the MPAL samples based on response to induction chemotherapy, including selective upregulation of the IL-16 pathway in relapsed samples.

CONCLUSIONS

We have for the first time described the single-cell transcriptomic landscape of pediatric MPAL and demonstrated that B/My and T/My MPAL have distinct scRNAseq profiles from each other, AML, and ALL. Differences in transcriptomic profiles were seen based on response to therapy, but larger studies will be needed to validate these findings.

Treatment of Relapsed B/T-cell Mixed Phenotype Acute Leukemia With Blinatumomab

Here, we describe the treatment of a patient with relapsed/refractory B/T mixed phenotype acute leukemia (MPAL) using blinatumomab monotherapy, the first bispecific T cell engager (BiTE) approved by the FDA for relapsed/refractory B cell acute lymphoblastic leukemia (B-ALL). A 64-year-old man with a history of stage 3 chronic kidney disease and type 2 diabetes mellitus was discovered to have B/T MPAL on bone marrow biopsy during hospitalization for dyspnea due to pulmonary embolism. The patient achieved brief remission with blinatumomab treatment before succumbing to neutropenic sepsis. The lack of sufficient data to guide therapy in MPAL remains a challenge, highlighting the potential of new targeted approaches such as blinatumomab to improve outcomes in relapsed/refractory MPAL.

Multicenter retrospective analysis of clinical outcome of adult patients with mixed-phenotype acute leukemia treated with acute myeloid leukemia-like or acute lymphoblastic leukemia-like chemotherapy and impact of allogeneic stem cell transplantation: a Campus ALL study

Mixed-phenotype acute leukemia (MPAL) is a rare disease. Treatment is often similar to that of acute lymphoblastic leukemia (ALL), but the outcome in adults and the role of allogeneic stem cell transplantation (AlloSCT) are not well defined. We report on 77 adult patients diagnosed with MPAL over the last 10 years and treated with a curative intent. Median age was 49 years; 7.6% of cases had a BCR::ABL1 rearrangement. Thirty patients (39%) were treated with an acute myeloid leukemia (AML)-like induction and 47 (61%) with an ALL-like scheme. The complete remission (CR) rate was 67.6% and an ALL-like therapy was associated with a better CR rate (P = 0.048). The median OS was 41.9 months; age ≤ 60 years was associated with a better OS (67 vs 26 months, P = 0.014). An AlloSCT was performed in 50 patients (65%). The 5-year OS of transplanted patients was 54%. The OS post-AlloSCT was better in patients who were minimal residual disease (MRD)-negative prior to transplant (75.8% vs 45.2%, P = 0.06). This study shows that MPAL patients respond better to an ALL-like induction therapy; that consolidation therapy should include, whenever possible, an AlloSCT and that MRD negativity should be a primary endpoint of treatment.

Recognizing Minor Leukemic Populations with Monocytic Features in Mixed-Phenotype Acute Leukemia by Flow Cell Sorting Followed by Cytogenetic and Molecular Studies: Report of Five Exemplary Cases

Mixed-phenotype acute leukemia (MPAL), a rare and heterogeneous category of acute leukemia, is characterized by cross-lineage antigen expression. Leukemic blasts in MPAL can be represented either by one population with multiple markers of different lineages or by several single-lineage populations. In some cases, a major blast population may coexist with a smaller population that has minor immunophenotypic abnormalities and may be missed even by an experienced pathologist. To avoid misdiagnosis, we suggest sorting doubtful populations and leukemic blasts and searching for similar genetic aberrations. Using this approach, we examined questionable monocytic populations in five patients with dominant leukemic populations of B-lymphoblastic origin. Cell populations were isolated either for fluorescence in situ hybridization or for clonality assessment by multiplex PCR or next-generation sequencing. In all cases, monocytic cells shared the same gene rearrangements with dominant leukemic populations, unequivocally confirming the same leukemic origin. This approach is able to identify implicit cases of MPAL and therefore leads to the necessary clinical management for patients.

Management of children and adolescents with chronic myeloid leukemia in blast phase: International pediatric CML expert panel recommendations

Treatment of chronic myeloid leukemia has improved significantly with the introduction of tyrosine kinase inhibitors (TKIs), and treatment guidelines based on numerous clinical trials are available for chronic phase disease. However for CML in the blast phase (CML-BP), prognosis remains poor and treatment options are much more limited. The spectrum of treatment strategies for children and adolescents with CML-BP has largely evolved empirically and includes treatment principles derived from adult CML-BP and pediatric acute leukemia. Given this heterogeneity of treatment approaches, we formed an international panel of pediatric CML experts to develop recommendations for consistent therapy in children and adolescents with this high-risk disease based on the current literature and national standards. Recommendations include detailed information on initial diagnosis and treatment monitoring, differentiation from Philadelphia-positive acute leukemia, subtype-specific selection of induction therapy, and combination with tyrosine kinase inhibitors. Given that allogeneic hematopoietic stem cell transplantation currently remains the primary curative intervention for CML-BP, we also provide recommendations for the timing of transplantation, donor and graft selection, selection of a conditioning regimen and prophylaxis for graft-versus-host disease, post-transplant TKI therapy, and management of molecular relapse. Management according to the treatment recommendations presented here is intended to provide the basis for the design of future prospective clinical trials to improve outcomes for this challenging disease.

Prognostic factors and outcomes of infant acute lymphoblastic leukemia (ALL), hypodiploid ALL, and mixed-phenotype acute leukemia (MPAL) in Canada: a report from CYP-C

The epidemiology of infant acute lymphoblastic leukemia (ALL), hypodiploid ALL, and mixed-phenotype acute leukemia (MPAL) in Canada is unknown. The main objective was to describe the prevalence, prognostic factors, and outcomes of three rare and high-risk ALL subtypes in Canada. This is a retrospective study using the Cancer in Young People-Canada (CYP-C) database. Event-free survival (EFS) and overall survival (OS) were described by the Kaplan-Meier method and compared using the log-rank test. Among 2626 children aged 0-14 years diagnosed with B-cell acute lymphoblastic leukemia (B-ALL) between 2001 and 2018, 227 (8.6%) patients were identified to be infant ALL (n = 139), hypodiploid ALL (n = 43), or MPAL (n = 45). The 5-year EFS/OS was significantly worse in the infant ALL subgroup compared to that of hypodiploid ALL and MPAL. For the entire cohort, presenting White blood cells (WBCs) ≥50 × 10⁹/L was independently associated with worse EFS/OS.

The Role of Gender-Related Immune Genes in Childhood Acute Myeloid Leukemia

The study of immune genes and immune cells is highly focused in recent years. To find immunological genes with prognostic value, the current study examines childhood acute myeloid leukemia according to gender. The TARGET database was used to gather the "mRNA expression profile data" and relevant clinical data of children with AML. To normalize processing and find differentially expressed genes (DEG) between male and female subgroups, the limma software package is utilized. We identified prognostic-related genes and built models using LASSO, multivariate Cox, and univariate Cox analysis. The prognostic significance of prognostic genes was then examined through the processing of survival analysis and risk score (RS) calculation. We investigated the connections between immune cells and prognostic genes as well as the connections between prognostic genes and medications. Finally, five immune genes from the TARGET database have been identified. These immune genes are considerably correlated to the prognosis of male patients.

Mixed-Phenotype Acute Leukemia: Clinical Diagnosis and Therapeutic Strategies

Mixed-phenotype acute leukemia (MPAL) comprises a heterogenous group of leukemias that are genetically, immunophenotypically, and clinically, diverse. Given the rarity of the disease, the diagnosis and treatment of MPAL is extremely challenging. Recent collaborative efforts have made significant progress in understanding the complex genomic landscape of MPAL. Some retrospective studies support starting ALL-type induction followed by an allogeneic stem cell transplant(allo-sct) in the first complete remission; however, due to the inherent bias of retrospective data and small case series, a prospective validation of AML- and ALL-based regimen, and the incorporation of targeted therapies based on genetics and immunophenotype are warranted. The prognosis of adults and children with MPAL varies; this justifies modulating the intensity of therapy, including the use of allo-sct as a consolidation strategy.

Characteristics, Treatment Complexity, and Outcome of Mixed-Phenotype Acute Leukemia in Children in a Low–Middle-Income Country

Background

Mixed-phenotype acute leukemia (MPAL) in children is an uncommon subtype of acute leukemia that cannot be definitively assigned to a specific lineage. There is no consensus on the best approach to therapy. Management is more complex in low–middle-income countries (LMICs).

Aim

To evaluate the clinicopathological characteristics and outcomes of patients with MPAL in a developing country.

Patients and Methods

A retrospective descriptive study of 42 pediatric patients newly diagnosed with MPAL from July 2007 until December 2017.

Results

The immunophenotyping was T/Myeloid in 24 patients (57.1%) and B/Myeloid in 16 (38.1%). Three subjects had MLL gene rearrangement, two had Philadelphia-positive chromosomes, and eight had FMS-like tyrosine kinase 3 (FLT3-ITD) internal tandem duplication (FLT3-ITD) with a ratio &gt;0.4. Two subjects died before starting chemotherapy. Ten patients (25%) received acute lymphoblastic leukemia (ALL) induction, and all achieved complete remission (CR) with no induction deaths and no shift of therapy. Thirty patients (75%) started therapy with acute myeloid leukemia (AML) induction: five (16.6%) died during induction, 17 (56.7%) achieved CR, and 10 patients received maintenance ALL therapy after ending AML treatment. Four of the eight patients with induction failure were switched to ALL therapy. The 5-year event-free survival (EFS) and overall survival (OS) rates were 56.7% [standard error (SE): 8.1%] and 61% (SE: 8%), while the cumulative incidence of relapse was 21.7% (SE: 6.7%), with a median follow-up duration of 5.8 years. Patients treated with ALL-directed therapy had a 5-year EFS rate of 111 70% (SE: 14%) and OS rate of 78.8% (SE: 13%). Patients treated with ALL-directed therapy had a 5-year EFS rate of 70% (SE: 14.5%) and OS rate of 78.8% (SE: 13%). FLT3-ITD mutation showed a significantly lower 5-year EFS rate of 28.6% (SE: 17%) vs. 75% (SE: 9%) for the wild type, p = 0.032. Undernourished patients with a body mass index (BMI) z-score ≤-2 at presentation had a significantly lower 5-year EFS rate of 20% (SE: 17%) compared to 61.8% (SE: 8%) for patients with BMI z-score &gt;-2, p = 0.015.

Conclusion

This study supports ALL-directed therapy for pediatric MPAL in a setting of LMIC. Given the poor outcome of FLT3-ITD, the role of FLT3 inhibitor needs to be explored in this subset of cases.

Allogeneic Hematopoietic Stem Cell Transplantation for Children With Acute Lymphoblastic Leukemia: Shifting Indications in the Era of Immunotherapy

Pediatric acute lymphoblastic leukemia generally carries a good prognosis, and most children will be cured and become long-term survivors. However, a portion of children will harbor high-risk features at the time of diagnosis, have a poor response to upfront therapy, or suffer relapse necessitating more intensive therapy, which may include allogeneic hematopoietic stem cell transplant (HSCT). Recent advances in risk stratification, improved detection and incorporation of minimal residual disease (MRD), and intensification of upfront treatment have changed the indications for HSCT over time. For children in first complete remission, HSCT is generally reserved for those with the highest risk of relapse. These include patients with unfavorable features/cytogenetics who also have a poor response to induction and consolidation chemotherapy, usually reflected by residual blasts after prednisone or by detectable MRD at pre-defined time points. In the relapsed setting, children with first relapse of B-cell ALL are further stratified for HSCT depending on the time and site of relapse, while all patients with T-cell ALL are generally consolidated with HSCT. Alternatives to HSCT have also emerged over the last decade including immunotherapy and chimeric antigen receptor (CAR) T-cell therapy. These novel agents may spare toxicity while attempting to achieve MRD-negative remission in the most refractory cases and serve as a bridge to HSCT. In some situations, these emerging therapies can indeed be curative for some children with relapsed or resistant disease, thus, obviating the need for HSCT. In this review, we seek to summarize the role of HSCT in the current era of immunotherapy.

Pediatric Mixed-Phenotype Acute Leukemia: What's New?

Simple Summary

Pediatric mixed-phenotype leukemia is a rare form of blood cancer in children. In this review, we cover both the evolution of treatment over the past several years and outline new emerging concepts in this disease.

Abstract

Mixed-phenotype acute leukemias (MPAL) are rare in children and often lack consensus on optimal management. This review examines the current controversies and emerging paradigms in the management of pediatric MPAL. We examine risk stratification, outcomes of recent retrospective and prospective collaborative trials, and the role of transplantation and precision genomics, and outline emerging targets and concepts in this rare entity.

Clinical features and prognosis of children with acute leukemias of ambiguous lineage under different diagnostic criteria

OBJECTIVES

To study the clinical features and prognosis of children with acute leukemias of ambiguous lineage (ALAL) under different diagnostic criteria.

METHODS

A retrospective analysis was performed on the medical data of 39 children with ALAL who were diagnosed and treated from December 2015 to December 2019. Among the 39 children, 34 received treatment. According to the diagnostic criteria for ALAL by World Health Organization and European Group for the Immunological Characterization of Leukemias, the 39 children were divided into two groups: ALAL group (n=28) and myeloid expression group (n=11). The clinical features, treatment, and prognosis were compared between the two groups.

RESULTS

The 34 children receiving treatment had a 3-year event-free survival (EFS) rate of 75%±9% and an overall survival rate of 88%±6%. The children treated with acute myeloid leukemia (AML) protocol had a 3-year EFS rate of 33%±27%, those treated with acute lymphoblastic leukemia (ALL) protocol had a 3-year EFS rate of 78%±10%, and those who had no remission after induction with AML protocol and then received ALL protocol had a 3-year EFS rate of 100%±0% (P<0.05). The children with negative minimal residual disease (MRD) after induction therapy had a significantly higher 3-year EFS rate than those with positive MRD (96%±4% vs 38%±28%, P<0.05). Positive ETV6-RUNX1 was observed in the myeloid expression group, and positive BCR-ABL1, positive MLL-r, and hyperleukocytosis (white blood cell count ≥50×109/L) were observed in the ALAL group. There was no significant difference in the 3-year EFS rate between the myeloid expression and ALAL groups (100%±0% vs 66%±11%, P>0.05).

CONCLUSIONS

ALL protocol has a better clinical effect than AML protocol in children with ALAL, and positive MRD after induction therapy suggests poor prognosis. Hyperleukocytosis and adverse genetic changes are not observed in children with myeloid expression, and such children tend to have a good prognosis, suggesting that we should be cautious to take it as ALAL in diagnosis and treatment.

Toward the Cure of Acute Lymphoblastic Leukemia in Children in China

This study explored results of therapy of children with acute lymphoblastic leukemia (ALL) in China, recent progress, and challenges. Included are a survey of therapy outcomes of ALL in Chinese children nationwide, comparison of these data with global ALL therapy outcomes, analyses of obstacles to improving outcomes, and suggestions of how progress can be achieved. Therapy outcomes at many Chinese pediatric cancer centers are approaching those of resource-rich countries. However, nationwide outcomes still need improvement. Obstacles include suboptimal clinical trials participation, children without adequate health care funding, human resource shortages, especially physicians expert in pediatric hematology and oncology, and social-economic disparities. We suggest how these obstacles have been and continue to be remedied including expanded access to protocol-based therapy, improved supportive care, health care reforms, recruitment of trained personnel, and international collaborations. China has made substantial progress treating children with ALL. We envision even better outcomes in the near future.

DUX4r, ZNF384r and PAX5-P80R mutated B-cell precursor acute lymphoblastic leukemia frequently undergo monocytic switch

Recently, we described B-cell precursor acute lymphoblastic leukemia (BCP-ALL) subtype with an early switch to the monocytic lineage and the loss of the B-cell immunophenotype, including CD19 expression. Thus far, the genetic background has remained unknown. Among 726 children consecutively diagnosed with BCP-ALL, 8% patients experienced a switch detectable by flow cytometry (FC). Using exome and RNA sequencing, the switch was found to positively correlate with three different genetic subtypes: PAX5-P80R mutation (five cases with switch of five), rearranged (DUX4r) (30 cases of 41) and rearranged (ZNF384r) (four cases of ten). Expression profiles or phenotypic patterns correlated with genotypes, but within each genotype no cases who subsequently switched could be indentified. If switching was not taken into account, the B-cell-oriented FC assessment underestimated the minimal residual disease level. For patients with PAX5-P80R, a discordance between FC-determined and polymerase chain reactiondetermined minimal residual disease was found on day 15, resulting from a rapid loss of the B-cell phenotype. Discordance on day 33 was observed in all the DUX4r, PAX5-P80R and ZNF384r subtypes. Importantly, despite the substantial phenotypic changes, possibly even challenging the appropriateness of BCP-ALL therapy, the monocytic switch was not associated with a higher incidence of relapse and poorer prognosis in patients undergoing standard ALL treatment.

Update on Acute Leukemias of Ambiguous Lineage

Acute leukemias of ambiguous lineage are a heterogenous group of diseases that include acute undifferentiated leukemias and mixed-phenotype acute leukemias (MPALs). These leukemias pose a challenge for pathologists and clinicians alike in diagnosis, treatment, and further management. Recent genetic characterization has provided insights into their underlying biology and classification, and has offered potential for targeted therapies. This article addresses diagnosis of MPALs with examples of the most common pitfalls, recent comprehensive molecular studies, and advancement in treatment and follow-up modalities.

Outcomes of pediatric mixed phenotype acute leukemia treated with lymphoid directed therapy: Analysis of an institutional series from India

There is limited data regarding pediatric mixed phenotype acute leukemia (MPAL) and there is no global consensus on its management yet. In this retrospective study, we analyzed the outcomes of children diagnosed with MPAL at our institute. This study included children ≤ 14 years with MPAL who presented to a tertiary cancer center in India from January 1st 2009 to December 31st 2015. Over a seven-year period, 1390 patients with leukemia presented to our institute of which 22 patients (1.5%) had MPAL. Sixteen patients (72.7%) had B/myeloid leukemia, while 4 (18.1%) and 2 (9%) patients had T/myeloid and B/T leukemia respectively. Twenty-one patients were treated with a modified BFM ALL 95 protocol. 76.1% (n = 16) of patients had a good prednisolone response (GPR) on day 8 and end-of-induction (EOI) marrow was in remission in 90.5% (n = 19). A poor prednisolone response (PPR) on day 8 correlated with an inferior relapse-free survival (25% vs 79.5%, P=.025). The 4-year event-free survival (EFS) and overall survival (OS) for the entire group was 60.8% and 64.9% respectively while the EFS for patients who had a GPR and remission at the EOI (n = 15) was 80% as compared to 16.7% in patients with PPR or induction failure. Lymphoid directed chemotherapy is seen to have good survival outcomes in pediatric MPAL. However, a PPR on day 8 or a positive EOI marrow may be an indication for more aggressive treatment.

Mixed Phenotype Acute Leukemia, B/Myeloid (Bilineal and Biphenotypic), With t(2;22)(q35;q12);EWSR1-FEV

BACKGROUND

Ewing sarcoma breakpoint region 1 gene (EWSR1) rearrangements are largely associated with the Ewing sarcoma family of tumors.

OBSERVATIONS

We report the first case of infantile, mixed phenotype acute leukemia, B/myeloid (bilineal and biphenotypic [B-lymphoid and B-lymphoid/myeloid]), with a t(2;22)(q35;q12). The EWSR1-fifth Ewing variant gene fusion and nonsense mutation in STAG2 were detected by next-generation sequencing and markedly high expression of fifth Ewing sarcoma variant mRNA detected by quantitative reverse transcription polymerase chain reaction. The patient was treated with a combined myeloid/lymphoid leukemia regimen followed by allogeneic stem cell transplant and was in complete remission at 3.8-year follow-up.

CONCLUSIONS

Our case study underscores the importance of a comprehensive evaluation of acute leukemia and provides insights into the phenotype of EWSR1 rearranged neoplasms in the context of partner genes and cell type.

Mixed phenotype acute leukemia in a child associated with a NUP98-NSD1 fusion and NRAS p.Gly61Arg mutation

Background

Mixed phenotype acute leukemia (MPAL) is a rare subset of acute leukemia in the pediatric population associated with genetic alterations seen in both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML).

Case

We describe a patient with MPAL with a NUP98 (nucleoporin 98)‐NSD1 gene fusion (nuclear receptor binding SET domain protein1) and NRAS (neuroblastoma RAS viral oncogene homolog mutation) p.Gly61Arg mutation who was treated with upfront AML‐based chemotherapy, received hematopoietic stem cell transplant (HSCT), but unfortunately died from relapsed disease.

Conclusion

This case highlights the challenges faced in choosing treatment options in MPAL patients with complex genomics, with predominant myeloid features.

Prednisolone poor response is not an indication for HSCT in pediatric B-cell precursor acute lymphoblastic leukemia in first remission: results from JACLS ALL-02 study

Approximately 90% of pediatric acute lymphoblastic leukemia (ALL) cases are curable with intensified chemotherapy, but very high-risk patients may require hematopoietic stem cell transplantation (HSCT). A suitable indication for HSCT in the first complete remission (CR1) should be defined to protect patients from long-term complications. We report the outcomes of HSCT in CR1 from the Japan Association of Childhood Leukemia Study (JACLS) ALL-02 study and reassess indications for HSCT. Of 1114 patients, 71 (6.4%) received HSCT in CR1. Indications included high-risk cytogenetic abnormalities and non-CR on day 33. Patients with B-cell precursor (BCP) ALL and a prednisolone poor response (PPR) received HSCT when leukocyte antigen-matched siblings were available. The 4-year overall survival (OS) of transplanted patients was 78.8% (confidence interval 67.3-86.6). Multivariate analysis revealed that cord blood transplantation was associated with poor OS. For BCP-ALL patients with PPR who achieved CR1 after induction therapy, HSCT in CR1 showed excellent outcomes (4-year OS 90.9%) but demonstrated no survival advantage as the outcome with chemotherapy was also excellent (4-year OS 97.0%). This study suggests that in BCP-ALL patients PPR is not an indication for HSCT in CR1. Precise evaluation of treatment responses would increase sophistication of indications for HSCT in CR1.

Case Report: Targeting 2 Antigens as a Promising Strategy in Mixed Phenotype Acute Leukemia: Combination of Blinatumomab With Gemtuzumab Ozogamicin in an Infant With a KMT2A-Rearranged Leukemia

Mixed phenotype acute leukemia (MPAL) accounts for 2-5% of leukemia in children. MPAL are at higher risk of induction failure. Lineage switch (B to M or vice versa) or persistence of only the lymphoid or myeloid clone is frequently observed in biphenotypic/bilineal cases, highlighting their lineage plasticity. The prognosis of MPAL remains bleak, with an event-free survival (EFS) of less than 50% in children. A lymphoid-type therapeutic approach appears to be more effective but failures to achieve complete remission (CR) remain significant. KMT2A fusions account for 75-80% of leukemia in infants under one year of age and remains a major pejorative prognostic factor in the Interfant-06 protocol with a 6 years EFS of only 36%. The search for other therapeutic approaches, in particular immunotherapies that are able to eradicate all MPAL clones, is a major issue. We describe here the feasibility and tolerance of the combination of two targeted immunotherapies, blinatumomab and Gemtuzumab Ozogamicin, in a 4-year-old infant with a primary refractory KTM2A-rearranged MPAL. Our main concern was to determine how to associate these two immunotherapies and we describe how we decided to do it with the parents’ agreement. The good MRD response on the two clones made it possible to continue the curative intent with a hematopoietic stem cell transplant at 9 months of age. Despite a relapse at M11 post-transplant because of the recurrence of a pro-B clone retaining the initial lymphoid phenotype, the child is now 36 months old, in persistent negative MRD CR2 for 12 months after a salvage chemotherapy and an autologous CAR T cells infusion, with no known sequelae to date. This case study can thus lead to the idea of a sequential combination of two immunotherapies targeting two distinct leukemic subclones (or even a single biphenotypic clone), as a potential one to be tested prospectively in children MPAL and even possibly all KMT2A-rearranged infant ALL.

Mixed Phenotype Acute Leukemia: Current Approaches to Diagnosis and Treatment

PURPOSE OF REVIEW

Mixed phenotype acute leukemia (MPAL) is a rare subtype of acute leukemia with features of both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). The review examines current definitions and controversies in classification of MPAL, new insights into genomic drivers and pathogenesis, recent evidence to support treatment recommendations, and opportunities for future research.

RECENT FINDINGS

Recent collaborative efforts have made progress in understanding the genomic landscape and optimal therapy for MPAL. The preponderance of retrospective data supports beginning therapy with ALL directed regimens. Differences in prognosis for adult and children with MPAL have led to divergent approaches for therapy intensity, including use of stem cell transplantation consolidation. MPAL remains a challenging leukemia to understand, research, and treat due to low incidence, shifting and subjective approaches to classification, and innate biological heterogeneity. Ongoing research hopes to surmount these obstacles through prospective studies within large cooperative groups to provide new insight into targetable biology and further refine optimal therapy.

Cytogenetic aberration in mixed-phenotype acute leukemia in children: A single-center retrospective review

BACKGROUND

Mixed-phenotype acute leukemia (MPAL) poses a diagnostic and therapeutic dilemma. No consensus exists on the strategy to assign patients with MPAL to either lymphoid- or myeloid-directed treatment. Thus, a better understanding of the characteristics of MPAL is a crucial unmet need. This study aims to provide information on a population-based cohort of children who received treatment based on standard, simple immunophenotypic criteria.

METHODS

Single-center, retrospective clinical and laboratory reviews of patients with MPAL were provided by morphology, immunophenotyping, cytogenetics, and molecular methods. We identified 242 flow cytometry samples. Of all consecutive pediatric patients with acute leukemia, we identified 8 (3.3%) patients with MPAL fulfilling WHO 2016 criteria; these were classified as follows: B-lymphoid + myeloid (n = 4), T-lymphoid + myeloid (n = 2), and B + T-lymphoid (n = 2).

RESULTS

Of 8 MPAL cases, 4 were boys and 4 girls [median age at diagnosis: 10.8 (range 1.1-17) years]. The b3a2 (p210) and e1a2 (p190) BCR/ABL fusion transcripts were detected in 1 patient with B/myeloid MPAL. Regarding the morphology, all patients were initially diagnosed as acute lymphoblastic leukemia, but no morphological characteristics or cytogenetic aberration was particularly predictive of an MPAL. Furthermore, 4 of 8 patients (50%) with MPAL were associated with chromosome 21 monosomy or partial trisomy.

CONCLUSION

Despite no single recurrent chromosomal abnormality that could serve as a hallmark lesion in MPAL, cytogenetic alterations are frequent and predominantly associated with complex karyotype involving chromosome 21 abnormalities.

Value of flow cytometry for MRD-based relapse prediction in B-cell precursor ALL in a multicenter setting

PCR of TCR/Ig gene rearrangements is considered the method of choice for minimal residual disease (MRD) quantification in BCP-ALL, but flow cytometry analysis of leukemia-associated immunophenotypes (FCM-MRD) is faster and biologically more informative. FCM-MRD performed in 18 laboratories across seven countries was used for risk stratification of 1487 patients with BCP-ALL enrolled in the NOPHO ALL2008 protocol. When no informative FCM-marker was available, risk stratification was based on real-time quantitative PCR. An informative FCM-marker was found in 96.2% and only two patients (0.14%) had non-informative FCM and non-informative PCR-markers. The overall 5-year event-free survival was 86.1% with a cumulative incidence of relapse (CIR_5y) of 9.5%. FCM-MRD levels on days 15 (HzR 4.0, p < 0.0001), 29 (HzR 2.7, p < 0.0001), and 79 (HzR 3.5, p < 0.0001) associated with hazard of relapse adjusted for age, cytogenetics, and WBC. The early (day 15) response associated with CIR_5y adjusted for day 29 FCM-MRD, with higher levels in adults (median 2.4 × 10⁻² versus 5.2 × 10⁻³, p < 0.0001). Undetectable FCM- and/or PCR-MRD on day 29 identified patients with a very good outcome (CIR_5y = 3.2%). For patients who did not undergo transplantation, day 79 FCM-MRD > 10⁻⁴ associated with a CIR_5y = 22.1%. In conclusion, FCM-MRD performed in a multicenter setting is a clinically useful method for MRD-based treatment stratification in BCP-ALL.

The genomic and biological complexity of mixed phenotype acute leukemia

Mixed phenotype acute leukemia (MPAL) is a heterogeneous group of leukemias that are defined immunophenotypically by antigen expression on blasts of both myeloid and lymphoid lineage. With the exception of BCR-ABL positive and KMT2A rearranged MPAL, the biology of the majority of MPAL remains uncertain. Several recent studies have explored the genomic and epigenetic landscape of MPAL and have suggested a further refinement of the WHO classification to emphasize the genomic heterogeneity of MPAL. Further studies including single cell analysis, whole exome sequencing and time of flight cytometry will provide for further biological characterization. Treatment decisions are complicated due to this lack of classification and the dearth of prospective randomized studies. Acute lymphoblastic leukemia-type therapy appears to achieve higher remission rates, and allogenic stem cell transplantation may be beneficial in a select group of patients in first complete remission. Multi-center collaborations may answer these questions more conclusively. Our review aims to discuss the diagnostic challenges, recent genomic studies and therapeutic strategies in this poorly understood disease.

Pediatric acute lymphoblastic leukemia

The last decade has witnessed great advances in our understanding of the genetic and biological basis of childhood acute lymphoblastic leukemia (ALL), the development of experimental models to probe mechanisms and evaluate new therapies, and the development of more efficacious treatment stratification. Genomic analyses have revolutionized our understanding of the molecular taxonomy of ALL, and these advances have led the push to implement genome and transcriptome characterization in the clinical management of ALL to facilitate more accurate risk-stratification and, in some cases, targeted therapy. Although mutation- or pathway-directed targeted therapy (e.g., using tyrosine kinase inhibitors to treat Philadelphia chromosome [Ph]-positive and Phlike B-cell-ALL) is currently available for only a minority of children with ALL, many of the newly identified molecular alterations have led to the exploration of approaches targeting deregulated cell pathways. The efficacy of cellular or humoral immunotherapy has been demonstrated with the success of chimeric antigen receptor T-cell therapy and the bispecific engager blinatumomab in treating advanced disease. This review describes key advances in our understanding of the biology of ALL and optimal approaches to risk-stratification and therapy, and it suggests key areas for basic and clinical research.

Precision medicine in acute lymphoblastic leukemia

The cure rate of childhood acute lymphoblastic leukemia (ALL) has exceeded 90% in some contemporary clinical trials. However, the dose intensity of conventional chemotherapy has been pushed to its limit. Further improvement in outcome will need to rely more heavily on molecular therapeutic as well as immuno-and cellular-therapy approaches together with precise risk stratification. Children with ETV6-RUNX1 or hyperdiploid > 50 ALL who achieve negative minimal residual disease during early remission induction are suitable candidates for reduction in treatment. Patients with Philadelphia chromosome (Ph)-positive or Ph-like ALL with ABL-class fusion should be treated with dasatinib. BH3 profiling and other preclinical methods have identified several high-risk subtypes, such as hypodiplod, early T-cell precursor, immature T-cell, KMT2A-rearranged, Ph-positive and TCF-HLF-positive ALL, that may respond to BCL-2 inhibitor venetoclax. There are other fusions or mutations that may serve as putative targets, but effective targeted therapy has yet to be established. For other high-risk patients or poor early treatment responders who do not have targetable genetic lesions, current approaches that offer hope include blinatumomab, inotuzumab and CAR-T cell therapy for B-ALL, and daratumumab and nelarabine for T-ALL. With the expanding therapeutic armamentarium, we should start focus on rational combinations of targeted therapy with non-overlapping toxicities.

Clinicoepidemiologic Profile and Outcome Predicted by Minimal Residual Disease in Children With Mixed-phenotype Acute Leukemia Treated on a Modified MCP-841 Protocol at a Tertiary Cancer Institute in India

INTRODUCTION

Mixed-phenotype acute leukemia (MPAL) accounts for 1.2% to 5% of acute leukemia across age groups with intermediate prognosis. We evaluated clinicoepidemiologic profiles and outcomes of MPAL.

METHODS

Records of children younger than 15 years of age with acute leukemia from January 2010 to December 2016 were reviewed on the basis of the MPAL WHO 2008 criteria. Treatment was uniform with a modified MCP-841 protocol. Descriptive analysis tools were used. Outcomes were measured by the Kaplan-Meier method on MedCalc, version 14.8.1.

RESULTS

Among 3830 children with acute leukemia in the study period, 2892 received treatment from our center, of whom 24 (0.83%) had MPAL, median age 9 years, with a male:female ratio of 3:1, and median white blood cell of 13.4×10/L. Common immunophenotypes were B/myeloid-12 (50%), T/myeloid-9 (37.5%), and B/T-lymphoid-3 (12.5%). Some B/myeloid cases had abnormal cytogenetics. Seventeen patients were evaluable for outcome. Sixteen patients underwent postinduction bone marrow and 13 (81%) achieved morphologic remission. Thirteen patients underwent flow cytometry-based minimal residual disease evaluation; 9 (69%) were <0.01% (4 postinduction, 5 postconsolidation), and 67% of these had sustained remission till the last follow-up. None underwent bone marrow transplant. The projected 3-year event-free and overall survival rates were 40% and 48%, respectively (median follow-up: 22 mo).

CONCLUSION

MPAL represented <1% of childhood acute leukemia. acute lymphoblastic leukemia-type chemotherapy that incorporated high-dose cytarabine was effective in achieving an minimal residual disease-negativity rate of 69% in evaluated patients, which was also predictive of better outcome.

Favorable outcomes of acute leukemias of ambiguous lineage treated with hyperCVAD: a multi-center retrospective study

Acute leukemias of ambiguous lineage (ALAL) are rare hematologic malignancies with poor outcomes. Retrospective studies have suggested that acute lymphoblastic leukemia (ALL) regimens are more effective than acute myeloid leukemia (AML) regimens. We retrospectively examined the effectiveness of the widely-used adult ALL regimen hyperfractionated cyclophosphamide, vincristine, doxorubicin, and dexamethasone (hyperCVAD) as initial therapy in patients with ALAL at five academic institutions. Twenty-five patients were identified, including 23 with mixed phenotype acute leukemia (MPAL) and two with acute undifferentiated leukemia. Five of 8 tested (63%) had FLT3-ITD and 3 of 25 (12%) were Philadelphia chromosome-positive. The complete remission (CR) rate was 76%, with CR with incomplete count recovery (CRi) in an additional 8%, for an overall response rate of 84%. Median number of cycles to CR/CRi was 1. There were no deaths in the first 30 days. Of the 21 patients achieving CR or CRi, 14 (66%) proceeded to allogeneic hematopoietic stem cell transplantation. With a median follow-up time of 31.6 months, median overall survival for the entire cohort was not reached, and the estimated 2-year survival was 63%. HyperCVAD can be considered an effective and tolerable front-line regimen for patients with ALAL, and warrants further prospective study.

The Biology of B-Progenitor Acute Lymphoblastic Leukemia

Genomic analyses have revolutionized our understanding of the biology of B-progenitor acute lymphoblastic leukemia (ALL). Studies of thousands of cases across the age spectrum have revised the taxonomy of B-ALL by identifying multiple new subgroups with diverse sequence and structural initiating events that vary substantially by age at diagnosis and prognostic significance. There is a growing appreciation of the role of inherited genetic variation in predisposition to ALL and drug responsiveness and of the nature of genetic variegation and clonal evolution that may be targeted for improved diagnostic, risk stratification, disease monitoring, and therapeutic intervention. This review provides an overview of the current state of knowledge of the genetic basis of B-ALL, with an emphasis on recent discoveries that have changed our approach to diagnosis and monitoring.

Optimal therapeutic strategies for mixed phenotype acute leukemia

PURPOSE OF REVIEW

Mixed phenotype acute leukemia (MPAL) encompasses a rare group of clinically, immunophenotypically, and genetically diverse leukemias. Diagnosing and treating these patients remains challenging. In recent years, systematic efforts have been made to better define the genetic landscape of MPAL. These insights allow better understanding of the pathophysiology of MPAL, have the potential for a more biologically meaningful classification and may promote targeted, novel approaches to treat these leukemias.

RECENT FINDINGS

Recent studies suggest that MPALs originate in a multipotent primitive cell, demonstrate large genetic diversity and include subgroups that may benefit from targeted therapy. Recent data support the use of ALL-type induction followed by allogeneic stem cell transplantation in first remission for most adults. Novel targeted approaches hold promise for treatment of MPAL; however, some may unpredictably select for clonal expansion of cells from a different lineage than observed at presentation.

SUMMARY

A biologically and genetically driven classification of MPAL may yield more accurate prognosis and potentially direct therapy in patients with MPAL. Prospective efforts that incorporate targeted approaches based on genetics and immunophenotype are warranted.

Diagnostic workup of acute leukemias of ambiguous lineage

Acute leukemias of ambiguous lineage (ALAL) comprise acute undifferentiated leukemias (AUL) and mixed-phenotype acute leukemias (MPAL). In the revised fourth edition of the World Health Organization (WHO) classification provided further refinements to the diagnostic criteria for ALAL. Molecular characterization of MPALs using comprehensive next-generation sequencing (NGS) has provided insights into their underlying biology and enabled a deeper understanding of ALAL classification. This review addresses the various components of pathologic assessment to establish a diagnosis of ALAL, and to further subclassify individual cases as AUL or MPAL, with an emphasis on the most up-to-date revisions to diagnostic criteria. In addition, key issues related to the detection of minimal residual disease (MRD) in ALALs and MPALs, and recently uncovered novel molecular diagnostic findings that may be helpful in better distinguishing various types of MPALs from each other, and from their "non-mixed" phenotypic correlates, are also discussed.

Mixed phenotype acute leukemia: Biological profile, clinical characteristic and treatment outcomes: Report of the population-based study

OBJECTIVES

The aim of this population-based, retrospective study was to analyze biological and clinical features and treatment results in children diagnosed with MPAL in all Polish pediatric oncology centers between 2007 and 2018.

METHODS

Among 2893 children and adolescents diagnosed and treated for acute leukemia, 39 (1.35%) patients fulfilled the WHO criteria of MPAL. The T/myeloid phenotype was most prevalent.

RESULTS

Cytogenetics findings were seen in 2 (5.1%), while chromosomal abnormalities were found in 14 (35.9%) patients. Thirty-two patients achieved CR-1, including 23 (92.0%) treated with ALL-directed chemotherapy and 9 (64.3%) treated with AML-type induction regimens. Within these patients, 4 (12.5%) died due to treatment-related complications and 11 (34.4%) relapsed. Nineteen (63.3%) patients underwent allo-HSCT in CR-1 and 14 (73.7%) of them have been in CR-1. In total, 17 (43.6%) patients remain in CR-1 for 1-12 years, including 14 (58.3%) with T/myeloid MPAL. The 5-year pOS and pEFS were 51.8% and 44.2%, respectively. The overall survival for ALL-directed therapy was significantly better than the one for AML-type chemotherapy (P = .001). It was also better for patients who underwent HSCT in CR-1 (P = .001).

CONCLUSIONS

The prognosis of MPAL is unsatisfactory, but initial treatment with ALL-directed chemotherapy consolidated with allo-HSCT improves the outcomes in MPAL.

Significance of minimal residual disease in pediatric mixed phenotype acute leukemia: a multicenter cohort study

The rarity of mixed phenotype acute leukemia (MPAL) has precluded adequate data to incorporate minimal residual disease (MRD) monitoring into therapy. Fluidity in MPAL classification systems further complicates understanding its biology and outcomes; this includes uncertainty surrounding the impact of shifting diagnostic requirements even between iterations of the World Health Organization (WHO) classification. Our primary objective was to address these knowledge gaps. To do so, we analyzed clinicopathologic features, therapy, MRD, and survival in a centrally-reviewed, multicenter cohort of MPAL uniformly diagnosed by the WHO classification and treated with acute lymphoblastic leukemia (ALL) regimens. ALL induction therapy achieved an EOI MRD negative (<0.01%) remission in most patients (70%). EOI MRD positivity was predictive of 5-year EFS (HR = 6.00, p < 0.001) and OS (HR = 9.57, p = 0.003). Patients who cleared MRD by EOC had worse survival compared with those EOI MRD negative. In contrast to adults with MPAL, ALL therapy without transplantation was adequate to treat most pediatric patients. Earlier MRD clearance was associated with better treatment success and survival. Prospective trials are now necessary to validate and refine MRD thresholds within the pediatric MPAL population and to identify salvage strategies for those with poor predicted survival.