Emergence of clonal cytogenetic abnormalities in Ph- cells in some CML patients in cytogenetic remission to imatinib but restoration of polyclonal hematopoiesis in the majority

The Contemporary Role of Hematopoietic Stem Cell Transplantation in the Management of Chronic Myeloid Leukemia: Is It the Same in All Settings?

Hematopoietic stem cell transplantation (HSCT) for chronic myeloid leukemia (CML) patients has transitioned from the standard of care to a treatment option limited to those with unsatisfactory tyrosine kinase inhibitor (TKI) responses and advanced disease stages. In recent years, the threshold for undergoing HSCT has increased. Most CML patients now have life expectancies comparable to the general population, and therefore, the goal of therapy is shifting toward achieving treatment-free remission (TFR). While TKI discontinuation trials in CML show potential for achieving TFR, relapse risk is high, affirming allogeneic HSCT as the sole curative treatment. HSCT should be incorporated into treatment algorithms from the time of diagnosis and, in some patients, evaluated as soon as possible. In this review, we will look at some of the recent advances in HSCT, as well as its indication in the era of aiming for TFR in the presence of TKIs in CML.

An interesting case of chronic myeloid leukemia with twists and turns

Additional cytogenetic abnormalities (ACA) are known to crop up in Ph⁺ cells of chronic myeloid leukemia (CML) patients due to cytogenetic evolution. But the frequency of molecular evolution and ACA is much less in Ph^- cells of CML patients and is poorly understood. We report an interesting and rare case of Ph⁺ CML, who progressed to B lymphoblastic crisis, achieved remission, and later developed Ph^- acute myeloid leukemia (AML) with KMT2A gene rearrangement and no detectable BCR- ABL transcripts.

Secondary Acute Myeloid Leukemia in a Chronic Myeloid Leukemia Patient in Deep Molecular Response—An Unusual Case Report

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder that develops from the stem cell compartment. The classical translocation (BCR-ABL1) is present in approximately 95% of CML patients. Through disease progression, clonal evolution with additional chromosomal abnormalities (ACAs) start appearing. Although relatively rare, chromosomal abnormalities can exist or develop in the Philadelphia (Ph)-negative clones, which may lead to the evolution of myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). We hereby present a case of AML which emerged from a Ph-negative clone in a patient with a history of CML who was in deep molecular response. The possible mechanisms of ACAs have been discussed.

Genetic Biomarkers in Chronic Myeloid Leukemia: What Have We Learned So Far?

Chronic Myeloid Leukemia (CML) is a rare malignant proliferative disease of the hematopoietic system, whose molecular hallmark is the Philadelphia chromosome (Ph). The Ph chromosome originates an aberrant fusion gene with abnormal kinase activity, leading to the buildup of reactive oxygen species and genetic instability of relevance in disease progression. Several genetic abnormalities have been correlated with CML in the blast phase, including chromosomal aberrations and common altered genes. Some of these genes are involved in the regulation of cell apoptosis and proliferation, such as the epidermal growth factor receptor (EGFR), tumor protein p53 (TP53), or Schmidt-Ruppin A-2 proto-oncogene (SRC); cell adhesion, e.g., catenin beta 1 (CTNNB1); or genes associated to TGF-β, such as SKI like proto-oncogene (SKIL), transforming growth factor beta 1 (TGFB1) or transforming growth factor beta 2 (TGFB2); and TNF-α pathways, such as Tumor necrosis factor (TNFA) or Nuclear factor kappa B subunit 1 (NFKB1). The involvement of miRNAs in CML is also gaining momentum, where dysregulation of some critical miRNAs, such as miRNA-451 and miRNA-21, which have been associated to the molecular modulation of pathogenesis, progression of disease states, and response to therapeutics. In this review, the most relevant genomic alterations found in CML will be addressed.

Additional chromosomal abnormalities at chronic myeloid leukemia diagnosis predict an increased risk of progression

At diagnosis of chronic-phase chronic myeloid leukemia (CML), there are conflicting data as to whether additional cytogenetic abnormalities (ACAs) beyond a standard Philadelphia (Ph) translocation confer a higher risk of subsequent disease progression. In the United Kingdom SPIRIT2 trial comparing imatinib 400 mg daily with dasatinib 100 mg daily, diagnostic karyotypes were available in 763 of the 814 patients recruited. Of these, 27 had ACAs in either/both the original 4 major route group (trisomy 8 or 19, iso17q or a second Ph) or the 5 additional lesions recently described (trisomy 21, 3q26.2, monosomy 7/7q-, 11q23, and complex karyotypes), and their progression rate was significantly higher (22.2%) than in patients without one of these ACAs (2.2%; P < .001). Patients with ACAs had worse progression-free survival (PFS; hazard ratio [HR], 5.21; 95% confidence interval [CI], 2.59-10.50; P < .001) and freedom from progression (FFP; HR, 12.66; 95% CI, 4.95-32.37; P < .001) compared with patients without ACAs. No association was seen between the Sokal or European Treatment and Outcome Study long-term survival (ELTS) scores and the presence of ACAs. Univariate analysis showed that higher Sokal and ELTS scores and the presence of ACAs were associated with poorer PFS, though only ACAs and high-risk ELTS scores were associated with poorer FFP. Multivariable models identified both the Sokal/ELTS score and ACAs as significant independent factors for PFS but only ELTS score and ACAs as significant independent factors for FFP. The data support the view that certain ACAs are predictive of disease progression independently of Sokal or ELTS scores.

Genetic Heterogeneity in Chronic Myeloid Leukemia: How Clonal Hematopoiesis and Clonal Evolution May Influence Prognosis, Treatment Outcome, and Risk of Cardiovascular Events

Chronic myeloid leukemia (CML) has long been considered as a model of cancer caused by a single-driver genetic lesion (BCR/ABL1 rearrangement) that codes for a unique, gain-of-function, deregulated protein. However, in the last decade, high-throughput sequencing technologies have shed light on a more complex genetic landscape, in which additional mutations may be found in different disease phases, including diagnosis. These genetic lesions may even precede the occurrence of the Philadelphia (Ph) chromosome, pointing to an antecedent premalignant state of clonal hematopoiesis (CH) at least in some patients. Preliminary data support the hypothesis that the most frequent CH-associated mutations (DNMT3A, TET2, and ASXL1) may be associated with a risk of vascular event, but a definitive answer for this topic is still lacking. Moreover, several recent studies have linked a much more complex genetic background in chronic-phase CML, including signs of clonal evolution over time, with depth of treatment responses or with patient survival. In the present review, we address the current state of the art on age-related CH, its association with cardiovascular risk, and its pathophysiology; review the current knowledge on CH that precedes the acquisition of the Ph chromosome in CML patients; and discuss available evidence on the prognostic and predictive value of additional mutations in chronic-phase CML, either as a sign of clonal dynamics under treatment or as markers of an antecedent CH.

Chronic Myeloid Leukemia: Modern therapies, current challenges and future directions

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm caused by a reciprocal translocation [t(9;22)(q34;q11.2)] that leads to the fusion of ABL1 gene sequences (9q34) downstream of BCR gene sequences (22q11) and is cytogenetically visible as Philadelphia chromosome (Ph). The resulting BCR/ABL1 chimeric protein is a constitutively active tyrosine kinase that activates multiple signaling pathways, which collectively lead to malignant transformation. During the early (chronic) phase of CML (CP-CML), the myeloid cell compartment is expanded, but differentiation is maintained. Without effective therapy, CP-CML invariably progresses to blast phase (BP-CML), an acute leukemia of myeloid or lymphoid phenotype. The development of BCR-AB1 tyrosine kinase inhibitors (TKIs) revolutionized the treatment of CML and ignited the start of a new era in oncology. With three generations of BCR/ABL1 TKIs approved today, the majority of CML patients enjoy long term remissions and near normal life expectancy. However, only a minority of patients maintain remission after TKI discontinuation, a status termed treatment free remission (TFR). Unfortunately, 5-10% of patients fail TKIs due to resistance and are at risk of progression to BP-CML, which is curable only with hematopoietic stem cell transplantation. Overcoming TKI resistance, improving the prognosis of BP-CML and improving the rates of TFR are areas of active research in CML.

Development of Philadelphia chromosome-negative acute myeloid leukemia with IDH2 and NPM1 mutations in a patient with chronic myeloid leukemia who showed a major molecular response to tyrosine kinase inhibitor therapy

Tyrosine kinase inhibitors (TKIs) are standard therapies for chronic myeloid leukemia (CML) that can eradicate Ph-positive leukemic cells. However, disease control is not achievable in a minority of cases, most commonly due to evolution of TKI-resistant clones. There have also been rare cases of emergence of Ph-negative clones with other cytogenetic abnormalities, and, less commonly, development of Ph-negative acute myeloid leukemia (AML), whose molecular pathogenesis is largely unknown. Here we report molecular features of a patient with Ph + CML who developed Ph-negative AML after showing a major molecular response to dasatinib. A 55-year-old man was diagnosed with CML. He achieved a complete cytogenetic response three months after dasatinib therapy but developed AML with normal karyotype 1 year later. After receiving induction and consolidation chemotherapy for AML, the patient achieved complete remission with no evidence of CML under maintenance with bosutinib. Targeted sequencing of serial bone marrow samples identified mutations in IDH2 and NPM1 in the Ph-negative AML cells, which had not been detected in CML cells. These results suggest that Ph-negative AML in this patient originated from a preleukemic population, which might have expanded during or after the successful elimination of CML clones with TKI therapy.

Chronic Myeloid Leukemia, Version 2.2021, NCCN Clinical Practice Guidelines in Oncology

Chronic myeloid leukemia (CML) is defined by the presence of Philadelphia chromosome (Ph) which results from a reciprocal translocation between chromosomes 9 and 22 [t(9;22] that gives rise to a BCR-ABL1 fusion gene. CML occurs in 3 different phases (chronic, accelerated, and blast phase) and is usually diagnosed in the chronic phase. Tyrosine kinase inhibitor therapy is a highly effective first-line treatment option for all patients with newly diagnosed chronic phase CML. This manuscript discusses the recommendations outlined in the NCCN Guidelines for the diagnosis and management of patients with chronic phase CML.

CML - Not only BCR-ABL1 matters

BCR-ABL1 is in the center of chronic myeloid leukemia (CML) pathology, diagnosis and treatment, as confirmed by the success of tyrosine kinase inhibitor (TKI) therapy. However, additional mechanisms and events, many of which function independently of BCR-ABL1, play important roles, particularly in terms of leukemic stem cell (LSC) persistence, primary and secondary resistance, and disease progression. Promising therapeutic approaches aim to disrupt pathways which mediate LSC survival during successful TKI treatment, in the hope of improving long-term treatment-free-remission and perhaps provide a functional cure for some patients. Over the years through advances in sequencing technology frequent molecular aberrations in addition to BCR-ABL1 have been identified not only in advanced disease but also in chronic phase CML, often affecting epigenetic regulators such as ASXL1, DNMT3A and TET2. Analyses of serial samples have revealed various patterns of clonal evolution with some mutations preceding the BCR-ABL1 acquisition. Such mutations can be considered to be important co-factors in the pathogenesis of CML and could potentially influence therapeutic strategies in the future.

The leukaemia stem cell: similarities, differences and clinical prospects in CML and AML

For two decades, leukaemia stem cells (LSCs) in chronic myeloid leukaemia (CML) and acute myeloid leukaemia (AML) have been advanced paradigms for the cancer stem cell field. In CML, the acquisition of the fusion tyrosine kinase BCR-ABL1 in a haematopoietic stem cell drives its transformation to become a LSC. In AML, LSCs can arise from multiple cell types through the activity of a number of oncogenic drivers and pre-leukaemic events, adding further layers of context and genetic and cellular heterogeneity to AML LSCs not observed in most cases of CML. Furthermore, LSCs from both AML and CML can be refractory to standard-of-care therapies and persist in patients, diversify clonally and serve as reservoirs to drive relapse, recurrence or progression to more aggressive forms. Despite these complexities, LSCs in both diseases share biological features, making them distinct from other CML or AML progenitor cells and from normal haematopoietic stem cells. These features may represent Achilles' heels against which novel therapies can be developed. Here, we review many of the similarities and differences that exist between LSCs in CML and AML and examine the therapeutic strategies that could be used to eradicate them.

Clinical implications of clonal chromosomal abnormalities in Philadelphia negative cells in CML patients after treated with tyrosine kinase inhibitors

Emergence of clonal chromosomal abnormalities in Philadelphia chromosome-negative (CCA/Ph-) cells in chronic myeloid leukemia (CML) patients during the treatment with tyrosine kinase inhibitors (TKIs) is an interesting phenomenon. Although previous studies revealed some potential impact of CCA/Ph- on CML patients' outcome, clinical significance of CCA/Ph- in CML patients remains to be further elucidated. We retrospectively reviewed the patients with CML evaluated at Genoptix Medical Laboratory in Carlsbad, California from 2005 to 2015. Twenty-four CML patients with CCA/Ph- cells were identified. These include 18 patients with single chromosomal abnormality, 4 patients with double chromosomal abnormalities, and two patients with complex cytogenetic abnormalities. In addition to trisomy 8 and monosomy 7, we identified that 20q- was also a common abnormality in CCA/Ph- cells. Most of the patients with CCA/Ph- cells demonstrated no significant dysplasia or increased blasts with two exceptions: one patient with persistent 7q- exhibiting mild dysmegakaryopoiesis, suggestive of an early evolving myelodysplastic syndrome, and another patient with complex cytogenetic abnormalities who developed acute myeloid leukemia after gained MLL amplification. One patient with complex cytogenetic abnormalities showed optimal response to TKI treatment, no overt dysplasia, and no disease progression during almost 4-years of follow-up. More interestingly, FISH tests could identify more cases with double chromosomal abnormalities and these cases showed suboptimal responses to TKI treatments. Our observation indicates that 20q- was also a common abnormality in CCA/Ph- cells, further FISH tests revealed additional CCA/Ph-, and the majority of CML patients with two or more chromosomal abnormalities in Ph- cells showed inferior response to TKI treatments. The results of our study suggest that CML cases with CCA/Ph- may represent a group of patients with heterogeneous genetic alterations.

[Philadelphia chromosome-negative myeloid neoplasms in patients with Philadelphia chromosome-positive chronic myeloid leukemia during tyrosine kinase inhibtor-therapy]

Objective: To compare the clinical features between the 2 cohorts developing myelodysplastic syndrome or acute myeIogenous Ieukemia in Philadelphia chromosome-negative cells (Ph(-) MDS/AML) and maintaining disease stable in the patients with Philadelphia chromosome-positive chronic myeloid Ieukemia (Ph(+) CML) who had clonal chromosomal abnormalities in Philadelphia chromosome-negative metaphases (CCA/Ph(-)) during tyrosine kinase inhibtor (TKI) - therapy. Methods: We retrospectively analyzed Ph(+) CML patients who developed CCA/Ph(-) during TKI-therapy from May 2001 to December 2017. Results: Data of CCA/Ph(-) 63 patients, including 7 progressing to Ph(-) MDS/AML and 56 remaining disease stable were collected. Compared with those with stable disease, patients with Ph(-)MDS/AML had lower hemoglobin (P=0.007) and platelet (P=0.006) counts, and higher proportion of peripheral blasts (P<0.001) when the first time CCA/Ph(-) was detected, and more mosonomy 7 abnormality (5/7, 71.4%) when MDS or AML was diagnosed; meanwhile, trisomy 8 (32/56, 57.1%) was more common in those with stable disease. Outcome of the patients with Ph(-) MDS/AML were poor. However, most of those with CCA/Ph(-) and stable disease had optimal response on TKI-therapy. Conclusions: A few patients with Ph(+) CML developed CCA/Ph(-) during TKI-therapy, most of them had stable disease, but very few patients developed Ph(-) MDS/AML with more common occurrence of monosomy 7 or unknown cytopenia. Our data suggested the significance of monitoring of peripheral blood smear, bone marrow morphology and cytogenetic analysis once monosomy 7 or unknown cytopenia occurred.

Occurrence of chromosomal abnormalities in Philadelphia chromosome-negative metaphases in patients with chronic-phase chronic myeloid leukemia undergoing TKI treatments

Forty-three chromosomal abnormalities in Philadelphia-negative metaphases (Ph-CAs) appeared in 35 of 432 patients in chronic phase chronic myeloid leukemia (CP-CML) undergoing tyrosine kinase inhibitor (TKI) treatments. These CAs were mostly common in trisomy-8 (16 cases), trisomy-Y (five cases), and monosomy-7 (five cases). Furthermore, Ph- CAs were significantly associated with higher platelet count (494 × 10⁹/L vs. 326 × 10⁹/L, p = .006), and higher incidence of true clonal evolution in Ph-positive metaphase (22.9% vs. 9.1%, p = .017). Additionally, patients with Ph- CAs had worse rates of complete cytogenetic remission (76% vs. 86%, p = .0091), major molecular remission (55% vs. 76%, p = .001), progression-free survival (47% vs. 86%, p < .001), but a similar overall survival rates compared to those in patients without Ph- CAs. In conclusion, Ph- CAs may predict worse response to TKI therapies and survival in patients with CP-CML, thus requiring close cytogenetic monitoring.

When to Consider Allogeneic Transplantation in CML

Tyrosine kinase inhibitor (TKI) therapy has radically altered the treatment strategy for chronic myeloid leukemia. Allogeneic transplantation, which over a decade ago was considered the definitive therapy for CML, is now appropriately used in cases where all TKIs are not tolerated, in cases of resistance to TKI therapy, or when the disease progresses from chronic phase to accelerated or blast phase.

Dasatinib and Azacitidine Followed by Haploidentical Stem Cell Transplant for Chronic Myeloid Leukemia with Evolving Myelodysplasia: A Case Report and Review of Treatment Options

BACKGROUND CML presenting with a variant Philadelphia translocation, atypical BCR-ABL transcript, additional chromosomal aberrations, and evolving MDS is uncommon and therapeutically challenging. The prognostic significance of these genetic findings is uncertain, even as singular aberrations, with nearly no data on management and outcome when they coexist. MDS evolving during the course of CML may be either treatment-associated or an independently coexisting disease, and is generally considered to have an inferior prognosis. Tyrosine kinase inhibitors (TKI) directed against BCR-ABL are the mainstay of treatment for CML, whereas treatment modalities that may be utilized for MDS and CML include allogeneic stem cell transplant and - at least conceptually - hypomethylating agents. CASE REPORT Here, we describe the clinical course of such a patient, demonstrating that long-term combined treatment with dasatinib and azacitidine for coexisting CML and MDS is feasible and well tolerated, and may be capable of slowing disease progression. This combination therapy had no deleterious effect on subsequent potentially curative haploidentical bone marrow transplantation. CONCLUSIONS The different prognostic implications of this unusual case and new therapeutic options in CML are discussed, together with a review of the current literature on CML presenting with different types of genomic aberrations and the coincident development of MDS. Additionally, this case gives an example of long-term combined treatment of tyrosine kinase inhibitors and hypomethylating agents, which could be pioneering in CML treatment.

Diagnostic and prognostic cytogenetics of chronic myeloid leukaemia: an update

INTRODUCTION

Despite the advent of molecular assessment, banding cytogenetics and fluorescence in situ hybridization (FISH) still have a significant role in diagnostic and prognostic approaches to chronic myeloid leukaemia (CML). Area covered: At diagnosis and during treatment with tyrosine kinase inhibitors (TKIs), cytogenetics is used to detect the Philadelphia chromosome, with its typical translocation t(9;22)(q34;q11.2), and any additional or other chromosomal aberrations (ACAs and OCAs) that may arise in 5-10% of cases, the latter associated to transformation of the disease in blast phases. In this review, the potential role of banding cytogenetics and FISH is discussed through a review of published papers on the prognostic impact of these tools in CML treatment and monitoring. Expert commentary: Cytogenetic techniques, including banding cytogenetics and FISH, continue to maintain a crucial role in CML monitoring. At diagnosis and after 3 months of therapy, banding cytogenetics will continue to be an essential test to perform, but it will become redundant after the achievement of a major molecular response (MMR) assessed with molecular techniques. FISH analysis maintains its usefulness in monitoring the response to TKIs only in special situations.

Clonal chromosomal aberrations in Philadelphia negative cells such as monosomy 7 and trisomy 8 may persist for years with no impact on the long term outcome in patients with chronic myeloid leukemia

The appearance of clonal chromosomal aberrations in Philadelphia negative cells (CCA/Ph-) during the treatment of chronic myeloid leukemia (CML) was recently confirmed. Importance of these findings has not been clearly defined. We present data on the time of appearance, persistence, size of the CCA/Ph- clone in terms of drugs used and hematological, cytogenetic and molecular response rates. The focus was on the peripheral blood cytopenias and myelodysplastic changes in the bone marrow microscopic evaluation. In 5 out of 155 (3,2%) CML patients, the persistent presence (up to nine years) of CCA/Ph- was found (monosomy 7 and trisomy 8 in unrelated clones in two patients treated with tyrosine kinase inhibitors; trisomy 8 in two patients on imatinib; trisomy 21 in one patient on interferon alfa treatment). Aberrations were present in median 24% Ph- cells in 3-15 subsequent analyses at different cytogenetic and molecular response time points. No evident myelodysplastic changes nor transformation to MDS/AML occurred in patients with CCA/Ph-. All the patients achieved major molecular response (MMR). It seems that CCA/Ph- presence does not affect the long term outcome in patients with chronic myeloid leukemia. Further complex monitoring of the CML patients with CCA/Ph- is still needed.

Clinical course of patients with incidental finding of 20q- in the bone marrow without a morphologic evidence of myeloid neoplasm

Deletion of the long arm of chromosome 20 (20q-) is a frequent finding in bone marrow karyotypes, mainly associated with myeloid neoplasms (MNs). Its clinical significance in the setting of normal bone marrow morphology is unclear. We described the clinical characteristics, cytogenetic findings, and outcome of 102 such patients seen at our institution from 2000-2014. Their median age was 66 years. The indication for bone marrow biopsy was either unexplained cytopenias (48%) or hematologic cancer staging/reevaluation (52%). In 88 (86%) patients, 20q- was an isolated finding. Thirty-nine (38%) patients previously received chemotherapy and 88 (86%) had cytopenias at the time of 20q- finding. After a median of 35 months, 12 (13%) patients developed MNs: 10 myelodysplastic syndromes, one acute myeloid leukemia and one myeloproliferative neoplasm. None of 14 patients with normal blood counts, but 7 of 35 (20%) with mild cytopenias, and 5 of 53 (9%) with moderate/severe cytopenias developed MNs. We did not find an association between the number of metaphases with 20q- and the development of MN. The incidental finding of 20q- in the bone marrow generally does not portend an early stage MN. Particularly, those without cytopenias at the time of diagnosis may have a good prognosis. Am. J. Hematol. 91:556-559, 2016. © 2016 Wiley Periodicals, Inc.

Transient monosomy 7 in a chronic myelogenous leukemia patient during nilotinib therapy: a case report

Tyrosine kinase inhibitor treated chronic myelogenous leukemia patients with monosomy 7 arising in Philadelphia chromosome negative (Ph−) cells tend to evolve into MDS/AML. However, monosomy 7 in Ph− cells can be a transient finding, and it is not an absolute indication of the emergence of a new myeloid malignancy.

Chronic myeloid leukemia: Relevance of cytogenetic and molecular assays

Chronic myeloid leukemia (CML) is the prototype cytogenetic malignancy. Even before the development of basic G- and R-banding techniques, CML was found to be associated with a persistent chromosomal abnormality, the Philadelphia (Ph) chromosome. Banding technology later showed the marker chromosome to be a translocation between the breakpoint cluster region (BCR) on chromosome 22q11.2 and the Abelson proto-oncogene (ABL) on chromosome 9q34. Further advances in cytogenetic and molecular biology have also contributed to the understanding, diagnosis, and treatment of CML. Fluorescent in situ hybridization (FISH) has revealed cryptic translocations in most cases of Ph-negative CML. Additional rare chromosomal variant translocations have been discovered as well. The understanding of cytogenetic and molecular physiopathology of CML has led to the use of tyrosine kinase inhibitors as treatment for this disease with spectacular success. Over the 40 years since being identified as the first cytogenetic disease, CML has become the greatest success in translating the basic science of oncology into the treatment of patients with cancer. In this review we will not only summarize the biology of CML, recent progress in the delineation of mechanisms and treatment strategies, but also we will discuss the laboratory tools used for diagnosing CML, for monitoring during treatment and for revealing point mutations and additional chromosomal abnormalities. In doing so, we will describe in detail our individual research on CML, identifying why and how these tests were performed to help to explain CML subgroups and clinical significance of additional chromosomal abnormalities.

The implication of cancer progenitor cells and the role of epigenetics in the development of novel therapeutic strategies for chronic myeloid leukemia

SIGNIFICANCE

Chronic myeloid leukemia (CML) involves the malignant transformation of hematopoietic stem cells, defined largely by the Philadelphia chromosome and expression of the breakpoint cluster region-Abelson (BCR-ABL) oncoprotein. Pharmacological tyrosine kinase inhibitors (TKIs), including imatinib mesylate, have overcome limitations in conventional treatment for the improved clinical management of CML.

RECENT ADVANCES

Accumulated evidence has led to the identification of a subpopulation of quiescent leukemia progenitor cells with stem-like self renewal properties that may initiate leukemogenesis, which are also shown to be present in residual disease due to their insensitivity to tyrosine kinase inhibition.

CRITICAL ISSUES

The characterization of quiescent leukemia progenitor cells as a unique cell population in CML pathogenesis has become critical with the complete elucidation of mechanisms involved in their survival independent of BCR-ABL that is important in the development of novel anticancer strategies. Understanding of these functional pathways in CML progenitor cells will allow for their selective therapeutic targeting. In addition, disease pathogenesis and drug responsiveness is also thought to be modulated by epigenetic regulatory mechanisms such as DNA methylation, histone acetylation, and microRNA expression, with a capacity to control CML-associated gene transcription.

FUTURE DIRECTIONS

A number of compounds in combination with TKIs are under preclinical and clinical investigation to assess their synergistic potential in targeting leukemic progenitor cells and/or the epigenome in CML. Despite the collective promise, further research is required in order to refine understanding, and, ultimately, advance antileukemic therapeutic strategies.

Transient presence of clonal chromosomal aberrations in Ph-negative cells in patients with chronic myeloid leukemia remaining in deep molecular response on tyrosine kinase inhibitor treatment

Advancements in treatment of chronic myeloid leukemia (CML) turned this formerly fatal neoplasm into a manageable chronic condition. Therapy with tyrosine kinase inhibitors (TKIs) often leads to significant reduction of disease burden, known as the deep molecular response (DMR). Herein, we decided to analyze the cohort of CML patients treated in our center with TKIs, who obtain and retain DMR for a period longer than 24 months. The aim of the study was to evaluate the frequency of clonal cytogenetic aberrations in Philadelphia-negative (Ph-) cells in patients with DMR during TKI treatment. The analyzed data was obtained during routine molecular and cytogenetic treatment monitoring, using G-banded trypsin and Giemsa stain (GTG) karyotyping and reverse transcription quantitative PCR. We noticed that approximately 50% of patients (28 of 55) in DMR had, at some follow-up point, transient changes in the karyotype of their Ph- bone marrow cells. In 9.1% of cases (5 of 55), the presence of the same aberrations was observed at different time points. The most frequently appearing aberrations were monosomies of chromosomes 19, 20, 21, and Y. Statistical analysis suggests that the occurrence of such abnormalities in CML patients correlates with the TKI treatment time.

Molecular-defined clonal evolution in patients with chronic myeloid leukemia independent of the BCR-ABL status

To study clonal evolution in chronic myeloid leukemia (CML), we searched for BCR-ABL-independent gene mutations in both Philadelphia chromosome (Ph)-negative and Ph-positive clones in 29 chronic-phase CML patients by targeted deep sequencing of 25 genes frequently mutated in myeloid disorders. Ph-negative clones were analyzed in 14 patients who developed clonal cytogenetic abnormalities in Ph-negative cells during treatment with tyrosine kinase inhibitors (TKI). Mutations were detected in 6/14 patients (43%) affecting the genes DNMT3A, EZH2, RUNX1, TET2, TP53, U2AF1 and ZRSR2. In two patients, the mutations were also found in corresponding Ph-positive diagnostic samples. To further investigate Ph-positive clones, 15 randomly selected CML patients at diagnosis were analyzed. Somatic mutations additional to BCR-ABL were found in 5/15 patients (33%) affecting ASXL1, DNMT3A, RUNX1 and TET2. Analysis of individual hematopoietic colonies at diagnosis revealed that most mutations were part of the Ph-positive clone. In contrast, deep sequencing of subsequent samples during TKI treatment revealed one DNMT3A mutation in Ph-negative cells that was also present in Ph-positive cells at diagnosis, implying that the mutation preceded the BCR-ABL rearrangement. In summary, BCR-ABL-independent gene mutations were frequently found in Ph-negative and Ph-positive clones of CML patients and may be considered as important cofactors in the clonal evolution of CML.

Impressive thrombocytosis evolving in a patient with a BCR-ABL positive CML in major molecular response during dasatinib treatment unmasks an additional JAK2V617F

We present a case of a 42-year old female with the rare diagnosis of a myeloproliferative syndrome harboring both a BCR-ABL transclocation and a JAK2V617F mutation.

Initially diagnosed with a CML, the patient underwent treatment with imatinib followed by dasatinib. Despite a major molecular response, the patient developed a thrombocytosis. Molecular analyses revealed a heterozygous JAK2V617F mutation, which was detected retrospectively in the bone marrow at the time of CML diagnosis.

This case underlines the complexity of MPS pathogenesis. For the clinician, a JAK2 mutational screening should be performed in CML patients without hematological response in the absence of BCR-ABL.

Targeting developmental pathways in children with cancer: what price success?

Much of current cancer research is aimed at exploiting cancers' molecular addictions through targeted therapeutics, with notable successes documented in clinical trials. By their nature, these agents have different side-effect profiles than conventional chemotherapy drugs. Although few targeted agents have attained regulatory approval for use in children, paediatric oncologists are gaining experience with these drugs, which can have unique short-term and long-term effects in developing children that are unrecognised in adults. This Review summarises the rationale for targeted therapy, challenges in paediatric drug development, unique side-effect profiles of targeted agents, limited data from children treated with targeted agents, and implications of current knowledge and gaps therein. The demonstrated and potential effects of targeted therapies on normal tissue development and function are discussed. Future clinical trial design should include carefully considered assessment of the developmental effects of targeted therapy, and informed supportive-care recommendations.

Molecular diagnostics in chronic myeloid leukemia

With the progress of chronic myeloid leukemia (CML) therapy, the molecular tools used to diagnose and monitor patients have become sophisticated. Despite this, a complete physical examination, complete blood count and bone marrow biopsy with metaphase karyotyping remain standard at diagnosis. Fluorescence in situ hybridization or qualitative reverse transcription polymerase chain reaction are indicated to exclude BCR-ABL1 in Philadelphia chromosome-negative patients with clinically typical CML. Bone marrow karyotyping is the gold standard for monitoring patients on imatinib until achievement of complete cytogenetic response, when quantitative polymerase chain reaction (qPCR) for BCR-ABL1 becomes the method of choice. Quantitative PCR results must be interpreted within a clinical context, the preceding results and performance characteristics of the PCR assay. Expression of qPCR results on the international scale enables comparison of results from different laboratories. BCR-ABL1 kinase domain mutation screening has added another level of complexity that informs the management of some patients with imatinib resistance. Using the entire diagnostic CML armamentarium in a rational and economic fashion can be as challenging as choosing the right treatment. The aim here is to describe what is universally accepted and what is controversial and to provide an update on emerging technologies, while trying to keep an eye on the real world outside specialized centers.

Clonal cytogenetic abnormalities after tyrosine kinase inhibitor therapy in Ph+ ALL resolution after decitabine therapy

Mixed chimerism and presence of minimal residual disease after stem cell transplantation (SCT) usually predict leukemia recurrence. In Philadelphia chromosome positive (Ph+) leukemia tyrosine kinase inhibitors can restore remission. These agents can induce clonal cytogenetic abnormalities in the Philadelphia negative cell population (CCA/Ph-), which may rarely progress to acute myeloid leukemia. A child with Ph+ acute lymphoblastic leukemia showed mixed donor chimerism and persistent bcr-abl transcripts after a matched sibling SCT. There was no response to tyrosine kinase inhibitor (TKI) therapy, but she has remained hematologically normal for more than 5 years. CCA/Ph- was detected but resolved with hypomethylating therapy.

Karyotypic findings in chronic myeloid leukemia cases undergoing treatment

BACKGROUND:

Chronic myeloid leukemia (CML) is a clonal myeloproliferative expansion of primitive hematopoietic progenitor cells.

MATERIALS AND METHODS:

In the present study, CML samples were collected from various hospitals in Amritsar, Jalandhar and Ludhiana.

RESULTS:

Chromosomal alterations seen in peripheral blood lymphocytes of these treated and untreated cases of CML were satellite associations, double minutes, random loss, gain of C group chromosomes and presence of marker chromosome. No aberrations were observed in control samples. Karyotypic abnormalities have also been noted in the Ph-negative cells of some patients in disease remission.

CONCLUSION:

This is a novel phenomenon whose prognostic implications require thorough and systematic evaluation.

Telomere loss in Philadelphia-negative hematopoiesis after successful treatment of chronic myeloid leukemia: evidence for premature aging of the myeloid compartment

Telomere shortening, a well-known marker of aging and cellular stress, occurs under several conditions in the hematopoietic compartment, including aplastic anemia and following iatrogenic noxae. We decided to verify whether pathological telomere erosion also arises in restored Philadelphia-negative (Ph-negative) hematopoiesis following successful treatment of chronic myeloid leukemia (CML). Eighty-one CML patients in complete cytogenetic remission were compared to 76 age-matched healthy subjects. Myeloid cells of CML patients had shorter telomeres than controls (6521 bp vs 7233 bp, p<0.001). This difference was specific for the myeloid compartment, since it was not observed in lymphoid cells (6774 bp vs 6909 bp, p=0.620). Acquired Ph-negative cytogenetic abnormalities (p=0.010), lack of complete molecular remission (p=0.016) and age (p=0.013) were independent predictors of telomere shortening. Telomere dynamics were assessed over a median follow-up period of 22 months. We documented accelerated non-physiological ongoing telomere shortening in 17/59 CML patients (28%). Patients experiencing grade 2-4 hematological toxicity, during CML remission possessed significantly shorter telomeres compared to those lacking toxicity (p=0.005 for any toxicity, p=0.007 for anemia). CML patients suffer from significant and often ongoing telomere stress resulting in premature and selective aging of the myeloid compartment which might have long-term consequences on function and integrity of Ph-negative hematopoiesis.

How I treat CML blast crisis

Blast crisis (BC) remains the major challenge in the management of chronic myeloid leukemia (CML). It is now generally accepted that BC is the consequence of continued BCR-ABL activity leading to genetic instability, DNA damage, and impaired DNA repair. Most patients with BC carry multiple mutations, and up to 80% show additional chromosomal aberrations in a nonrandom pattern. Treatment with tyrosine kinase inhibitors has improved survival in BC modestly, but most long-term survivors are those who have been transplanted. Patients in BC should be treated with a tyrosine kinase inhibitor according to mutation profile, with or without chemotherapy, with the goal of achieving a second chronic phase and proceeding to allogeneic stem cell transplantation as quickly as possible. Although long-term remissions are rare, allogeneic stem cell transplantation provides the best chance of a cure in BC. Investigational agents are not likely to provide an alternative in the near future. In view of these limited options, prevention of BC by a rigorous and early elimination of BCR-ABL is recommended. Early response indicators should be used to select patients for alternative therapies and early transplantation. Every attempt should be made to reduce or eliminate BCR-ABL consistent with good patient care as far as possible.

The first case of Philadelphia chromosome-negative acute promyelocytic leukemia following imatinib for chronic myelogenous leukemia

In chronic myelogenous leukemia, chromosomal abnormalities in Philadelphia-negative cells are rare and usually transient, but can infrequently lead to myelodysplastic syndrome and/or acute myeloid leukemia. We report an 82-ear-old patient with an 11-year history of chronic myelogenous leukemia, in complete cytogenetic response, who developed Philadelphia-negative t(15;17)/PMLRARA acute promyelocytic leukemia. This isolated case reaffirms several important clinicopathologic and biologic aspects of chronic myelogenous leukemia, and sheds a unique light on its Philadelphia-negative hematopoiesis. It also underlines the importance of continued cytogenetic monitoring of patients in complete cytogenetic response for the emergence of new chromosomal abnormalities.

Chronic myeloid leukemia: current perspectives

Chronic myeloid leukemia (CML), characterized by the t(9;22) and BCR/ABL1 fusion, is a disease model for studying the mechanisms of genetic abnormalities in leukemogenesis. The detection of the t(9;22), characterization of the BCR/ABL fusion, and the discovery of imatinib have elegantly reflected the success of our research efforts in CML. However, genomic instabilities that lead to the formation of the BCR/ ABL1 fusion are not fully understood. It is important to understand how various genes that are involved in regulating the signaling pathway and epigenetic deregulation cooperate with the BCR/ABL1 fusion in the initiation and progression of CML.