Predicting early blast transformation in chronic-phase chronic myeloid leukemia: is immunophenotyping the missing link?

Accelerated-phase CML: de novo and transformed

Despite the dramatic improvements in outcomes for the majority of chronic myeloid leukemia (CML) patients over the past 2 decades, a similar improvement has not been observed in the more advanced stages of the disease. Blast phase CML (BP-CML), although infrequent, remains poorly understood and inadequately treated. Consequently, the key initial goal of therapy in a newly diagnosed patient with chronic phase CML continues to be prevention of disease progression. Advances in genomic investigation in CML, specifically related to BP-CML, clearly demonstrate we have only scratched the surface in our understanding of the disease biology, a prerequisite to devising more targeted and effective therapeutic approaches to prevention and treatment. Importantly, the introduction of the concept of "CML-like" acute lymphoblastic leukemia (ALL) has the potential to simplify the differentiation between BCR::ABL1-positive ALL from de novo lymphoid BP-CML, optimizing monitoring and therapeutics. The development of novel treatment strategies such as the MATCHPOINT approach for BP-CML, utilizing combination chemotherapy with fludarabine, cytarabine, and idarubicin in addition to dose-modified ponatinib, may also be an important step in improving treatment outcomes. However, identifying patients who are high risk of transformation remains a challenge, and the recent 2022 updates to the international guidelines may add further confusion to this area. Further work is required to clarify the identification and treatment strategy for the patients who require a more aggressive approach than standard chronic phase CML management.

Abnormal B-lymphoblasts in myelodysplastic syndromes and myeloproliferative neoplasms other than chronic myeloid leukemia

BACKGROUND

Lineage infidelity is characteristic of mixed phenotype acute leukemia and is also seen in blast phase of chronic myeloid leukemia (CML), myeloid/lymphoid neoplasia with eosinophilia and gene rearrangements, and subtypes of acute myeloid leukemia. Driver genetic events often occur in multipotent progenitor cells in myeloid neoplasms, suggesting that multilineage output may be more common than appreciated. This phenomenon is not well studied in myelodysplastic syndrome (MDS) and non-CML myeloproliferative neoplasms (MPN).

METHODS

We systematically evaluated phenotypic lineage infidelity by reviewing bone marrow pathology and flow cytometry (FC) studies of 1262 consecutive patients with a diagnosis of MDS and/or non-CML MPN. We assessed B- and T-cells in these patients by FC. When abnormal B-lymphoblast (ABLB) populations were detected, we additionally evaluated immature B-cells using a high sensitivity FC assay for B-lymphoblastic leukemia/lymphoma (B-ALL).

RESULTS

We identified 9 patients (7 MDS, 7/713, 1%; 2 non-CML MPN, 2/312, 0.6%; 0 in MDS/MPN) with low-level ABLB populations (0.012%-3.6% of WBCs in marrow) with abnormal immunophenotypes. Genetic studies on flow sorted cell populations confirmed that some ABLB populations were clonally related to myeloid blasts (4/6, 67%). On follow-up, ABLB populations in 8/9 patients remained stable or disappeared. Only 1 case progressed to B-ALL.

CONCLUSIONS

These findings demonstrate that phenotypically detectable abnormal immature B lineage output occurs in MDS and non-CML MPN, albeit rarely. While presence of ABLB does not necessarily reflect blast crisis, the underlying disease biology of our findings may ultimately be relevant to patient management and warrants further investigation.

The fifth edition of the World Health Organization Classification and the International Consensus Classification of myeloid neoplasms: evolving guidelines in the molecular era with practical implications

PURPOSE OF REVIEW

There have been major advances in our understanding of molecular pathogenesis of myeloid neoplasms, which prompt the updates in the classification of myeloid neoplasms in the fifth edition of World Health Organization Classification (WHO-5) and the new International Consensus Classification (ICC). The purpose of this review is to provide an overview of these two classification systems for myeloid neoplasms.

RECENT FINDINGS

The definition, classification, and diagnostic criteria in many myeloid entities have been refined in WHO-5 and ICC with improved understanding of morphology and integration of new genetic findings. Particularly, molecular and cytogenetic studies have been increasingly incorporated into the classification, risk stratification, and selection of therapy of myeloid neoplasms. Overall, despite some revisions and discrepancies between WHO-5 and ICC, the major categories of myeloid neoplasms remain the same. Further validation studies are warranted to fine-tune and, ideally, integrate these two classifications.

SUMMARY

Integration of clinical information, laboratory parameters, morphologic features, and cytogenetic and molecular studies is essential for the classification of myeloid neoplasms, as recommended by both WHO-5 and ICC.

International Consensus Classification of Myeloid Neoplasms and Acute Leukemias: integrating morphologic, clinical, and genomic data

The classification of myeloid neoplasms and acute leukemias was last updated in 2016 within a collaboration between the World Health Organization (WHO), the Society for Hematopathology, and the European Association for Haematopathology. This collaboration was primarily based on input from a clinical advisory committees (CACs) composed of pathologists, hematologists, oncologists, geneticists, and bioinformaticians from around the world. The recent advances in our understanding of the biology of hematologic malignancies, the experience with the use of the 2016 WHO classification in clinical practice, and the results of clinical trials have indicated the need for further revising and updating the classification. As a continuation of this CAC-based process, the authors, a group with expertise in the clinical, pathologic, and genetic aspects of these disorders, developed the International Consensus Classification (ICC) of myeloid neoplasms and acute leukemias. Using a multiparameter approach, the main objective of the consensus process was the definition of real disease entities, including the introduction of new entities and refined criteria for existing diagnostic categories, based on accumulated data. The ICC is aimed at facilitating diagnosis and prognostication of these neoplasms, improving treatment of affected patients, and allowing the design of innovative clinical trials.

Incidence and immunophenotype of abnormal lymphoblast populations at diagnosis of chronic myeloid leukaemia in chronic phase

Chronic myeloid leukaemia most commonly presents in chronic phase (CML-CP) and it is characterised by granulocytic proliferation. Many patients have an excellent response to tyrosine kinase inhibitor therapy; however, a small proportion will develop lymphoid or myeloid blast crisis, with inferior clinical outcomes. Detection of lymphoblasts at diagnosis of CML-CP has been reported in small case series with conflicting results on the risk of subsequent blast crisis. The aim of this study was to identify the incidence and immunophenotype of abnormal lymphoblast populations in CML-CP. Retrospective review of bone marrow flow cytometry results of consecutive patients with newly diagnosed CML-CP between June 2012 and February 2021 was performed. Lymphoblasts, myeloblasts, haematogones, and mature lymphocytes were evaluated. Fifty-nine patients had bone marrow flow cytometry results available for review. Abnormal lymphoblast populations were detected in four patients (7%) comprising 0.05–0.19% of bone marrow events. The immunophenotype was similar but distinct from haematogones. The most common distinguishing features of the abnormal lymphoblast populations were abnormally bright expression of CD19 or CD10, weak CD38 or aberrant CD20 expression on CD34 + cells. The clinical case of one of the patients with abnormal lymphoblasts detected at diagnosis who went on to subsequent blast crisis is discussed. Abnormal lymphoblasts can be identified in CML-CP and may be under-recognised. Their detection requires careful analysis in order to distinguish them from normal precursors. The clinical significance of such populations requires further study.

Understanding and Monitoring Chronic Myeloid Leukemia Blast Crisis: How to Better Manage Patients

Chronic myeloid leukemia (CML) is triggered primarily by the t(9;22) (q34.13; q11.23) translocation. This reciprocal chromosomal translocation leads to the formation of the BCR-ABL fusion gene. Patients in the chronic phase (CP) experience a good curative effect with tyrosine kinase inhibitors. However, cases are treatment refractory, with a dismal prognosis, when the disease has progressed to the accelerated phase (AP) or blast phase (BP). Until now, few reports have provided a comprehensive description of the mechanisms involved at different molecular levels. Indeed, the underlying pathogenesis of CML evolution comprises genetic aberrations, chromosomal translocations (except for the Philadelphia chromosome), telomere biology, and epigenetic anomalies. Herein, we provide knowledge of the biology responsible for blast transformation of CML at several levels, such as genetics, telomere biology, and epigenetic anomalies. Because of the limited treatment options available and poor outcomes, only the therapeutic response is monitored regularly, which involves BCR-ABL transcript level assessment and immunologic surveillance, with the optimal treatment strategy for patients in CP adapted to evaluate disease recurrence or progression. Overall, selecting optimal treatment endpoints to predict survival and successful TFR improves the quality of life of patients. Thus, identifying risk factors and developing risk-adapted therapeutic options may contribute to a better outcome for advanced-phase patients.

Sudden blast phase in pediatric chronic myeloid leukemia-chronic phase with abnormal lymphoid blasts detected by flow cytometry at diagnosis: Can it be considered a warning sign?

BACKGROUND

Inconclusive knowledge persists regarding the course of chronic myeloid leukemia-chronic phase (CML-CP) patients with detectable abnormal blasts by flow-cytometry at diagnosis. The 2016 WHO classification is not specific regarding sub-classification of CML with <10% abnormal B-lymphoid blasts (ABLB), and suggests these patients often show rapid progression. We report the clinical course of pediatric CML-CP patients who had detectable abnormal blasts by flow-cytometry at baseline.

METHODS

Retrospective audit of all pediatric CML patients between January 2013 and December 2017 were included. Their clinical presentation, demographic profile, and treatment outcomes were extracted from electronic medical records. Some of these patients got flow-cytometry done by default, though it was not a routine part of diagnostic CML marrow studies.

RESULTS

Amongst 65 pediatric CML patients, flow-cytometry at initial diagnosis was available in 15 (CP-12; AP-3). Of the 12 CML-CP patients, 10 (83%) had abnormal flow-cytometric findings-5 (50%) with mixed lineage blasts (4-B/Myeloid, 1-B/T/Myeloid), and myeloid lineage blasts in the remaining 5 (50%). At a median follow-up of 26 months (range: 9-34 months), 3/5 patients with ABLB at diagnosis progressed to frank blast crisis (2 B-cell; 1 Mixed lineage). None among the five patients with diagnostic myeloid-alone aberrant blasts progressed to blast crisis. Imatinib resistant mutation was also found in 3/5 (60%) CML-CP patients with these ABLB at baseline.

CONCLUSIONS

Although a retrospective study with limited sample size, presence of ABLB detected on flow-cytometry in CML-CP patients, had a noticeable early conversion to CML-BC in our cohort. Incorporation of flow-cytometry in diagnostic work-up can provide useful insight regarding the behavior of pediatric CML-CP patients and guide therapy.

Cytogenetics-based risk prediction of blastic transformation of chronic myeloid leukemia in the era of TKI therapy

The high fatality of patients with blast phase (BP) chronic myeloid leukemia (CML) necessitates identification of high-risk (HR) patients to prevent onset of BP. Here, we investigated the risk of BP based on additional chromosomal abnormality (ACA) profiles in a cohort of 2326 CML patients treated with tyrosine kinase inhibitors (TKIs). We examined the time intervals from initial diagnosis to ACA emergence (interval 1), from ACA emergence to onset of BP (interval 2), and survival after onset of BP (interval 3). Based on BP risk associated with each ACA, patients were stratified into intermediate-1, intermediate-2, and HR groups, with a median duration of interval 2 of unreached, 19.2 months, and 1.9 months, respectively. There was no difference in durations of intervals 1 or 3 among 3 groups. Including patients without ACAs who formed the standard-risk group, the overall 5-year cumulative probability of BP was 9.8%, 28.0%, 41.7%, and 67.4% for these 4 groups, respectively. The pre-BP disease course in those who developed BP was similar regardless of cytogenetic alterations, and 84.4% of BP patients developed BP within the first 5 years of diagnosis. In summary, interval 2 is the predominant determinant of BP risk and patient outcome. By prolonging the duration of interval 2, TKI therapy mitigates BP risk associated with low-risk ACAs or no ACAs but does not alter the natural course of CML with HR ACAs. Thus, we have identified a group of patients who have HR of BP and may benefit from timely alternative treatment to prevent onset of BP.

Prognostic factors and survival outcomes in patients with chronic myeloid leukemia in blast phase in the tyrosine kinase inhibitor era: Cohort study of 477 patients

BACKGROUND

Outcomes in patients with chronic myeloid leukemia in blast phase (CML-BP) are historically dismal. Herein, the authors sought to analyze the characteristics, prognostic factors, and survival outcomes in patients with CML-BP in the tyrosine kinase inhibitor (TKI) era.

METHODS

A total of 477 patients with CML-BP were treated with a TKI at some point during the course of their CML. Cox proportional hazard models identified characteristics that were predictive of survival. Overall survival and failure-free survival were assessed. Optimal cutoff points for specific parameters were identified using classification and regression tree (CART) analysis.

RESULTS

The median age of the patients was 53 years (range, 16-84 years) and 64% were male. Approximately 80% of patients initially were diagnosed in the chronic phase of CML at a median of 41 months (range, 0.7-298 months) before transformation to CML-BP. De novo CML-BP occurred in 71 patients. Approximately 72% of patients received TKI therapy before CML-BP. The initial therapy for CML-BP included a TKI alone (35%), a TKI with chemotherapy (46%), and non-TKI therapies (19%). The median overall survival was 12 months and the median failure-free survival was 5 months. In multivariate analysis, myeloid immunophenotype, prior TKI, age ≥58 years, lactate dehydrogenase level ≥1227 IU/L, platelet count < 102 K/μL, no history of stem cell transplantation, transition to BP from chronic phase/accelerated phase, and the presence of chromosome 15 aberrations predicted for a significantly increased risk of death. Achievement of major hematologic response and/or complete cytogenetic response to first-line treatment was found to be predictive of better survival. The combination of a TKI with intensive chemotherapy followed by stem cell transplantation appeared to confer the best outcome.

CONCLUSIONS

Patients with CML-BP continue to pose a therapeutic challenge, have dismal outcomes, and require newer treatment approaches. Cancer 2017;123:4391-402. © 2017 American Cancer Society.

Flow Cytometric Measurement of Blood Cells with BCR-ABL1 Fusion Protein in Chronic Myeloid Leukemia

Chronic myeloid leukemia (CML) is characterized in the majority of cases by a t(9;22)(q34;q11) translocation, also called the Philadelphia chromosome, giving rise to the BCR-ABL1 fusion protein. Current treatment with tyrosine kinase inhibitors is directed against the constitutively active ABL1 domain of the fusion protein, and minimal residual disease (MRD) after therapy is monitored by real-time quantitative PCR (RQ-PCR) of the fusion transcript. Here, we describe a novel approach to detect and enumerate cells positive for the BCR-ABL1 fusion protein by combining the in situ proximity ligation assay with flow cytometry as readout (PLA-flow). By targeting of the BCR and ABL1 parts of the fusion protein with one antibody each, and creating strong fluorescent signals through rolling circle amplification, PLA-flow allowed sensitive detection of cells positive for the BCR-ABL1 fusion at frequencies as low as one in 10,000. Importantly, the flow cytometric results correlated strongly to those of RQ-PCR, both in diagnostic testing and for MRD measurements over time. In summary, we believe this flow cytometry-based method can serve as an attractive approach for routine measurement of cells harboring BCR-ABL1 fusions, also allowing simultaneously assessment of other cell surface markers as well as sensitive longitudinal follow-up.

Pediatric chronic myeloid leukemia with inv(3)(q21q26.2) and T lymphoblastic transformation: a case report

Background

Chronic myeloid leukemia (CML) comprises ~3 % of pediatric leukemia. Although therapy with tyrosine kinase inhibitors (TKIs) is highly effective for CML, multiple factors have been identified as predictive of treatment failure. Chromosomal abnormalities involving the MECOM locus at 3q26 portend therapy resistant disease in adults, yet have never been described in pediatric patients and have not been associated with T lymphoblastic progression.

Case presentation

We present a case of an 11-year-old boy with CML possessing the unique combination of T lymphoblastic transformation and a subclone harboring inv(3)(q21q26.2) at diagnosis. This is the first reported case of pediatric CML with inv(3)(q21q26.2) and the first case of T lymphoblastic progression associated with this karyotype. The patient was treated with single agent TKI therapy with robust initial response. Marrow histology at one month showed restoration of trilineage hematopoiesis and BCR-ABL RT-PCR at three months showed a 1.4 log reduction in transcript levels.

Conclusions

The karyotypic abnormality of inv(3)(q21q26.2) in CML is not restricted to adult patients. Moreover, while chromosome 3 abnormalities are markers of TKI resistance in adults, our patient showed a robust early response to single agent TKI therapy. This finding suggests pediatric CML with inv(3)(q21q26.2) may have distinct features and more favorable treatment responses than those described in adults.

Isolated Ocular Manifestation of Relapsed Chronic Myelogenous Leukemia Presenting as Myeloid Blast Crisis in a Patient on Imatinib Therapy: A Case Report and Review of the Literature

Blast phase in chronic myelogenous leukemia (CML) has rarely been reported to involve extramedullary sites like skin, lymph nodes, and central nervous system. Clinical history, characteristic hematologic findings (elevated leukocyte counts, myelocytic predominance, and basophilia), and Philadelphia chromosome are of high diagnostic significance especially in isolated extramedullary presentations. We describe a unique case of CML relapse with blast phase involving the eye. A 66-year-old man with a known diagnosis of CML on imatinib and in molecular remission for 3 years presented with a painful blind eye. Histologic examination revealed diffuse involvement of choroid, iris, vitreous humor, and the optic nerve by blast cells. The blasts expressed CD34, aberrant TdT, and a myeloid phenotype (CD13, CD33, and CD117). Fluorescence in situ hybridization (FISH) of vitreous fluid detected BCR-ABL1 gene rearrangement. Additionally, trisomy 8 and gains of 9 and 22 were seen which were not present in the initial diagnostic marrow study 3 years ago. At relapse, the bone marrow, peripheral blood, and the cerebrospinal fluid were not involved by CML. Patient received induction chemotherapy and single dose prophylactic intrathecal methotrexate and was maintained on antityrosine kinase therapy and eventually underwent allogenic stem cell transplantation.