Mixed-Phenotype Acute Leukemia: Clinical Diagnosis and Therapeutic Strategies

Acute leukemia of ambiguous lineage: Diagnosis, prognosis and treatment

Acute leukemias of ambiguous lineage (ALAL) are an infrequent subtype of acute leukemias without clear evidence of differentiation to a one single cell lineage. Despite their rarity constitute a recognized subgroup in the recent international classifications, such as the WHO (World Health Organization) classification. Their diagnosis require highly specialized flow cytometry technology, and also cytogenetics and molecular techniques. The low frequency of the disease has made it difficult to find the best therapeutic strategy, due both to the lack of prospective studies and randomized trials, and to the heterogeneity of the published retrospective studies on follow-up and treatment. The group of ALAL has bad prognosis, and usually requires intensive strategies that include consolidation with allogeneic stem cell transplant as part of the treatment. The objective of this review was to analyze diagnosis, treatment and prognosis of this rare subtype of leukemias.

Molecular genetic characterization of mixed-phenotype acute leukemia (MPAL) with BCR::ABL1 fusion

BACKGROUND

Mixed-phenotype acute leukemia with BCR::ABL1 fusion (MPALBCR::ABL1), previously known as Philadelphia chromosome-positive mixed phenotype acute leukemia, is a heterogeneous group that is segregated into different subtypes based on WHO-HAEM5. The genetic profile of MPALBCR::ABL1 remains poorly defined due to its rarity.

METHODS

We conducted a retrospective study of 16 patients with MPALBCR::ABL1 and compared their clinical and laboratory profiles to 20 patients with AMLBCR::ABL1.

RESULTS

Compared to patients with AMLBCR::ABL with a median age of 64 years old, patients with MPALBCR::ABL1 were significantly younger at a median of 47 years old (P = 0.031) with similar white blood cell (WBC) count, hemoglobin (Hb) count, platelet (PLT) count, lactate dehydrogenase (LDH) levels, and bone marrow blast percentage. MPALBCR::ABL1 patients harboured a similar frequency of co-occurring additional cytogenetic abnormalities (ACA) compared to AMLBCR::ABL1 with monosomy 7 (25 %) being the most common ACA in MPALBCR::ABL1. The most commonly mutated gene in MPALBCR::ABL1 patients was RUNX1 at 45 %. The overall survival (OS) and event-free survival (EFS) between MPALBCR::ABL1 and AMLBCR::ABL1 significantly differed, conferring a better prognosis for patients with MPALBCR::ABL1.

CONCLUSION

Our results indicate that adult patients with MPALBCR::ABL1 present with younger age and may have better survival outcomes than patients with AMLBCR::ABL1. In addition, our next-generation sequencing (NGS) data indicates that RUNX1 is frequently mutated in B/myeloid MPALBCR::ABL1 compared to AMLBCR::ABL1. Future studies are warranted to further elucidate the role of RUNX1 in this disease.

Implications of an unusual acute leukaemia phenotype on the care of a South African Jehovah's Witness patient

An HIV-negative South African woman in her 50s presented to hospital with fatigue. She had no medical history and is a Jehovah's Witness. Her full blood count revealed macrocytic anaemia and severe thrombocytopenia. On smear review, there were ±66% blasts with no lineage discerning morphological features. Peripheral blood flow cytometry revealed a blast population that expressed B-cell (CD19 dim, cCD79a dim, CD10 dim, CD22 moderate), T/NK-cell (CD7) and myeloid markers (HLA-DR, CD33, CD117). However, antigen combinations did not fulfil the requirements for specific lineage assignment. The bone marrow aspirate and trephine biopsy were hypercellular with diffuse involvement of blasts. Myeloperoxidase positivity was subsequently confirmed on cytochemistry and immunohistochemistry. The final diagnosis was an acute myeloid leukaemia with expression of aberrant lymphoid markers and monocytic cytochemistry. Delays in lineage assignment can derail timely induction, shake patient confidence and postpone the doctor-patient treatment discussions. This is particularly important in already vulnerable populations.

Flow cytometric characterisation of acute leukaemia in adolescent and adult Ethiopians

Background

Flow cytometric characterisation of acute leukaemia is a key diagnostic approach for clinical management of patients, but is minimally practised in resource-constrained settings like Ethiopia.

Objective

This study aimed to determine the immunophenotypes of acute leukaemia by flow cytometry at Tikur Anbessa Specialised Hospital, Addis Ababa, Ethiopia.

Methods

A cross-sectional study was conducted on adolescent and adult inpatients consecutively admitted from April 2019 to June 2021. Peripheral blood samples were stained for surface and cytoplasmic markers, and analysed by four-colour flow cytometry.

Results

Of 140 cases aged 13 years to 76 years, 74 (53%) were men and 66 (47%) were women, 68 (49%) had acute lymphocytic leukaemia (ALL), 65 (46 %) had acute myelogenous leukaemia (AML), and 7 (5.0%) had acute leukaemia non-otherwise specified. Acute lymphocytic leukaemia was more common among adolescent and male cases; AML was more common among adult and female cases. Among ALL subtypes, B-cell acute lymphocytic leukaemia cases (73.5%) were more common than T-cell acute lymphocytic leukaemia (26.5%). A subset of acute leukaemia, CD19+/CD56+ AML was identified in 3 cases (6% of AML). Of the B-cell ALL cases, 21 (42%) were CD34+/CD10+/CD66c+, 10% were CD34+/CD10+/CD66c-, 32% were CD34-/CD10+, and 6% were CD34+/CD10-. An unexpectedly high number of T-cell ALL cases that lacked surface CD3 were observed to have significantly higher levels of aberrantly expressed myeloid markers.

Conclusion

We observed multiple phenotypes identifying subtypes of acute leukaemia cases, extending our previous studies in Ethiopia.

What this study adds

This study extends previous studies by describing phenotypically defined subsets of ALL and AML which, in addition to diagnosis, may have useful prognostic value for clinicians.

Menin Inhibitors: New Targeted Therapies for Specific Genetic Subtypes of Difficult-to-Treat Acute Leukemias

Menin (MEN1) is a well-recognized powerful tumor promoter in acute leukemias (AL) with KMT2A rearrangements (KMT2Ar, also known as MLL) and mutant nucleophosmin 1 (NPM1m) acute myeloid leukemia (AML). MEN1 is essential for sustaining leukemic transformation due to its interaction with wild-type KMT2A and KMT2A fusion proteins, leading to the dysregulation of KMT2A target genes. MEN1 inhibitors (MIs), such as revumenib, ziftomenib, and other active small molecules, represent a promising new class of therapies currently under clinical development. By disrupting the MEN1-KMT2Ar complex, a group of proteins involved in chromatin remodeling, MIs induce apoptosis and differentiation AL expressing KMT2Ar or NPM1m AML. Phase I and II clinical trials have evaluated MIs as standalone treatments and combined them with other synergistic drugs, yielding promising results. These trials have demonstrated notable response rates with manageable toxicities. Among MIs, ziftomenib received orphan drug and breakthrough therapy designations from the European Medicines Agency in January 2024 and the Food and Drug Administration (FDA) in April 2024, respectively, for treating R/R patients with NPM1m AML. Additionally, in November 2024, the FDA approved revumenib for treating R/R patients with KMT2Ar-AL. This review focuses on the pathophysiology of MI-sensitive AL, primarily AML. It illustrates data from clinical trials and discusses the emergence of resistance mechanisms. In addition, we outline future directions for the use of MIs and emphasize the need for further research to fully realize the potential of these novel compounds, especially in the context of specific genetic subtypes of challenging AL.

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.

Leukemia cutis as an initial presentation in a case of mixed phenotype acute leukemia: a double jeopardy

Leukemia cutis (LC) is defined as infiltration of the skin by leukemic cells resulting in clinically recognizable cutaneous lesions. The lesions range from violaceous papules, plaques, nodules, blisters, maculopapular rash and as erythroderma. LC can precede or happen after the presentation of leukemia. Here, we report a case of Mixed phenotype Acute leukemia (MPAL) presenting as LC (erythematous & violaceous nodules) which is a rare as well as a grave combination as it carries a worse prognosis. Here, we present a case of MPAL which presented as Leukemia Cutis proven on biopsy. The paper discusses the importance of identifying LC both in a clinical and a pathological pretext as it is important to start the Chemotherapy for MPAL at the earliest for a better outcome.

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.

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.

Genetic Characterization of Pediatric Mixed Phenotype Acute Leukemia (MPAL)

BACKGROUND/AIM

Mixed phenotype acute leukemia (MPAL) is a rare hematologic malignancy in which the leukemic cells cannot be assigned to any specific lineage. The lack of well-defined, pathogenetically relevant diagnostic criteria makes the clinical handling of MPAL patients challenging. We herein report the genetic findings in bone marrow cells from two pediatric MPAL patients.

PATIENTS AND METHODS

Bone marrow cells were examined using G-banding, array comparative genomic hybridization, RNA sequencing, reverse transcription polymerase chain reaction, Sanger sequencing, and fluorescence in situ hybridization.

RESULTS

In the first patient, the genetic analyses revealed structural aberrations of chromosomal bands 8p11, 10p11, 11q21, and 17p11, the chimeras MLLT10::PICALM and PICALM::MLLT10, and imbalances (gains/losses) on chromosomes 2, 4, 8, 13, and 21. A submicroscopic deletion in 21q was also found including the RUNX1 locus. In the second patient, there were structural aberrations of chromosome bands 1p32, 8p11, 12p13, 20p13, and 20q11, the chimeras ETV6::LEXM and NCOA6::ETV6, and imbalances on chromosomes 2, 8, 11, 12, 16, 19, X, and Y.

CONCLUSION

The leukemic cells from both MPAL patients carried chromosome aberrations resulting in fusion genes as well as genomic imbalances resulting in gain and losses of many gene loci. The detected fusion genes probably represent the main leukemogenic events, although the gains and losses are also likely to play a role in leukemogenesis.

Superior sagittal sinus thrombosis in the course of mixed phenotype acute leukaemia treated with acute lymphoblastic leukaemia-like therapy-a case report

Mixed phenotype acute leukaemia (MPAL) is associated with worse overall survival, compared with other acute leukaemias in adults. Lack of clear treatment guidelines makes the therapy challenging. ALL-like induction and consolidation treatment followed by allo-HSCT is the preferred first-line treatment. We present a case of a 36-year-old woman diagnosed with MPAL (EGIL Myelo/B) with KMT2A rearrangement, treated with the PALG-ALL-7 (including PEG-asparaginase) protocol. On day 25 after the induction therapy initiation, numbness of limbs and dizziness were observed. Therefore, the imaging studies (CT and MRI) were performed and a diagnosis of thrombosis of superior sagittal sinus of the brain was established. Routinely performed blood coagulation tests showed prolonged APTT and PT, decreased antithrombin III activity and decreased free protein S concentration. LMWH treatment and substitutional therapy with antithrombin III were started, which resulted in a significant reduction in the thrombosis associated symptoms and improvement of the neurological status after 3 days. After induction and consolidation therapy, the patient obtained complete haematological remission and negative measurable residual disease. Six months after the diagnosis, allo-HSCT was successfully performed. During the 4 months follow-up, the patient remained MRD negative and thrombotic symptoms free. To the best of our knowledge, our communication has been the first report of such complication in an MPAL patient treated with PEG-asparaginase containing protocol in adults. We recommend increased vigilance in patients manifesting any mild neurological symptoms and early decision about the MRI study performance.

A Rare Case of Therapy-Related B-cell Acute Lymphoblastic Leukemia Arising From Acute Myeloid Leukemia

Therapy-related acute lymphoblastic leukemia (t-ALL) is a rare potential complication of chemotherapy. We describe the case of a 47-year-old male patient who was originally diagnosed with t(8;21) positive acute myeloid leukemia (AML) in 2019, received chemotherapy, achieved remission, and was disease-free for the next two years. During a routine follow-up in 2022, he was found to have developed subclinical pancytopenia, and further studies indicated a diagnosis of pH-negative, near-tetraploid B-cell acute lymphoblastic leukemia (B-ALL) that was positive for a Tier 1 TP53 mutation, consistent with t-ALL. The patient had a prolonged treatment course complicated by social factors, such as the impact of both disease and treatment on his ability to work enough to make a living and live life with the quality he desired. The patient elected to pause treatment and resume it at a later date, after which, unfortunately, significant disease progression occurred and the patient died from complicating neutropenic sepsis and variceal bleeding. This case illustrates the challenges of managing social circumstances and patient goals in the setting of medically necessary but potentially harsh treatment courses. Given the aggressive nature of t-ALL and its overall poor prognosis, goals of care must be re-evaluated and discussed often to ensure alignment of therapy with a patient's wishes.

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.