Genomic BCR-ABL1 breakpoints in pediatric chronic myeloid leukemia

Which Is the Best Tyrosine Kinase Inhibitor for Newly Diagnosed Chronic Myelogenous Leukemia?

The choice of frontline therapy for a patient with chronic phase chronic myeloid leukemia (CP-CML) can have a profound effect on the long-term clinical outcome. Currently, five tyrosine kinase inhibitors (TKIs-imatinib, dasatinib, nilotinib, bosutinib, and asciminib) are available for frontline therapy, but no single TKI is optimal for all patients. EUTOS long-term survival (ELTS) risk score, comorbidities, and treatment-free remission (TFR) priority are the key determinants of frontline TKI selection. Higher ELTS score, low age and comorbidity score, and a high priority for achievement of TFR would all favor the frontline use of a more potent TKI than imatinib. However, no TKI has improved survival compared with imatinib. In children with CP-CML, imatinib, dasatinib, and nilotinib have similar long-term efficacy, with ease of administration and impact of toxicities on quality of life being key considerations. Recent adult trials of reduced-dose dasatinib frontline showed that efficacy may be equivalent to standard-dose dasatinib with a better tolerability and safety profile, but experience is limited in patients with high-risk ELTS scores. The ASC4FIRST trial has confirmed that tolerability and molecular response with asciminib are superior to those with both imatinib and the second-generation (2G)-TKIs. While the overall treatment failure rate was lower with asciminib, the rate of BCR::ABL1 mutations that emerged with asciminib appeared to be higher. The risk of emergent mutations appears to be highly associated with the presence of ASXL1 mutations in the CML cells at diagnosis, but more work is needed to understand the implications of this finding.

NAMPT-mediated deacetylation of HCLS1 protein promotes clonogenic growth of pediatric CML cells

Pediatric chronic myeloid leukemia (CML) is a rare hematological malignancy with biological features that differ from that of adult patients. In pediatric CML patients the burden of tumor cells is higher resulting in a delayed achievement of deep molecular response (DMR) upon treatment with tyrosine kinase inhibitors (TKIs, e.g. imatinib) than what has been reported in adults. Therefore, the probability to develop resistance to TKIs in children with CML is higher than in adults due to much longer exposure to TKIs. Moreover, in children with CML, long-term treatment with imatinib causes hematologic and non-hematologic toxicities. Improvements of CML therapy in pediatric patients based on the targeting of hematopoiesis-specific BCR::ABL1 downstream effectors are needed. Here, we report elevated levels of the Nicotinamide phosphoribosyltransferase (NAMPT) in mononuclear cells of chronic phase CML (CP-CML) pediatric patients and in blastic phase CML cell lines. NAMPT inhibition abrogated in vitro clonogenic capacity and proliferation of CML cells. NAMPT deacetylates and activates the hematopoietic-specific lyn-substrate 1 (HCLS1) protein, which is essential for the proliferation of CML cells. Moreover, IL1RAP - a marker of myeloid leukemia initiating cells - and LEF-1 - a transcription factor of Wnt signaling - are downstream targets of NAMPT/HCLS1 pathway. Together, our results reveal new treatment avenues of pediatric CML patients by targeting NAMPT-mediated deacetylation of the hematopoietic-specific HCLS1 protein. Teaser Abstract Pediatric chronic myeloid leukemia (CML) patients need long-term tyrosine kinase inhibitor treatment which causes toxicities. Therefore, improvements of CML therapy in pediatric patients are needed. Here, we report elevated levels of the Nicotinamide phosphoribosyltransferase (NAMPT) in chronic phase pediatric CML cells. NAMPT inhibition abrogated in vitro clonogenic capacity and proliferation of CML cells. NAMPT deacetylates and activates the hematopoietic-specific lyn-substrate 1 (HCLS1) protein. Moreover, IL1RAP - a marker of myeloid leukemia initiating cells - is a downstream target of NAMPT/HCLS1 pathway. Together, our results reveal new treatment avenues of pediatric CML patients.

Genomic variant profiling in blast-phase paediatric chronic myeloid leukaemia: Predisposing and driving alterations

Paediatric blast-phase chronic myeloid leukaemia (CML-BP) is a rare and serious condition. Of 231 paediatric patients enrolled in the German CML-PAED-II registry between January 2007 and September 2023, 25 individuals (11%) were diagnosed with CML-BP. To identify genetic variants associated with early onset and disease transformation, we performed whole genome sequencing (WGS), deep targeted sequencing and cytogenetic analyses in 19 cases with de novo (n = 11) or secondary (n = 8) CML-BP and sufficient available biomaterial. Copy number variants (CNVs) were more frequent than single nucleotide variants (SNVs) and more prevalent in secondary than in de novo CML-BP. Recurrent pathogenic somatic SNVs were observed in ABL1 (n = 5, 24%), RUNX1 (n = 2, 12%) and ASXL1 (n = 2, 12%). Nine patients (47%) carried pathogenic germline (n = 8) or somatic (n = 1) variants in either of the genes ATM, CHEK2, FANCM, HERC2, NBN, RAD54B, RECQL4, SETD2 or TP63 belonging to the DNA damage response (DDR). Within a comparison cohort of 19 patients with chronic phase paediatric CML, only one individual (5%) exhibited a pathogenic DDR germline variant. Our study provides novel pathogenetic insights into paediatric CML-BP. The identification of pathogenic DDR-associated germline variants suggests a genetic predisposition with potential implications for patients and families concerning cancer treatment and surveillance.

Favorable outcomes of de novo advanced phases of pediatric chronic myeloid leukemia in the tyrosine kinase inhibitor era

Chronic myeloid leukemia (CML) is a rare disease during childhood, and accelerated phase (AP) and blast phase (BP) CML, also called advanced phases, are even rarer. We retrospectively collected and analyzed clinical data of children younger than 20 years with de novo advanced-phase CML between 1996 and 2017 in Japan. Median follow-up time was 8.9 years for AP-CML (n = 15) and 3.7 years for BP-CML (n = 32). The 5-year overall survival (OS) was 93.3% for AP-CML, and 100.0% for patients who received tyrosine kinase inhibitors (TKIs) in first-line therapy (n = 10). Four of the ten patients who received TKIs in first-line therapy remained in molecular remission without transplantation (median follow-up 5.5 years). The 5-year OS of patients with BP-CML was 79.0%, and most patients received chemotherapy before transplantation, with regimen selection based on blast immunophenotype. Furthermore, among patients who received transplantation after TKI therapy, the 5-year OS was 100.0% for AP and 84.8% for BP. In conclusion, our study confirmed excellent outcomes in children with de novo advanced-phase CML, especially in the TKI-era.

Distinct pattern of genomic breakpoints in CML and BCR::ABL1-positive ALL: analysis of 971 patients

BACKGROUND

The BCR::ABL1 is a hallmark of chronic myeloid leukemia (CML) and is also found in acute lymphoblastic leukemia (ALL). Most genomic breaks on the BCR side occur in two regions - Major and minor - leading to p210 and p190 fusion proteins, respectively.

METHODS

By multiplex long-distance PCR or next-generation sequencing technology we characterized the BCR::ABL1 genomic fusion in 971 patients (adults and children, with CML and ALL: pediatric ALL: n = 353; pediatric CML: n = 197; adult ALL: n = 166; adult CML: n = 255 patients) and designed "Break-App" web tool to allow visualization and various analyses of the breakpoints. Pearson's Chi-Squared test, Kolmogorov-Smirnov test and logistic regression were used for statistical analyses.

RESULTS

Detailed analysis showed a non-random distribution of breaks in both BCR regions, whereas ABL1 breaks were distributed more evenly. However, we found a significant difference in the distribution of breaks between CML and ALL. We found no association of breakpoints with any type of interspersed repeats or DNA motifs. With a few exceptions, the primary structure of the fusions suggests non-homologous end joining being responsible for the BCR and ABL1 gene fusions. Analysis of reciprocal ABL1::BCR fusions in 453 patients showed mostly balanced translocations without major deletions or duplications.

CONCLUSIONS

Taken together, our data suggest that physical colocalization and chromatin accessibility, which change with the developmental stage of the cell (hence the difference between ALL and CML), are more critical factors influencing breakpoint localization than presence of specific DNA motifs.

Treatment and follow-up of children with chronic myeloid leukaemia in chronic phase (CML-CP) in the tyrosine kinase inhibitor (TKI) era-Two decades of experience from the Tata Memorial Hospital paediatric CML (pCML) cohort

Tyrosine kinase inhibitors (TKIs) have drastically improved the outcomes of pCML (paediatric CML) but data on long-term off-target toxicities of TKIs in children are scarce. In this single-centre, retrospective cum prospective study of pCML in chronic phase, we report our experience of treating 173 children with imatinib and following them for long-term toxicities. Mean (SD) time to attain CHR, CCyR and MMR were 3.05 (2.1), 10.6 (8.4) and 43.4 (31.8) months respectively. DMR was not attained in 59 (34%) patients at last follow-up. Ten patients were switched to second-generation TKIs (2G-TKIs; nilotinib = 1/dasatinib = 9) due to poor/loss in response, of which seven had kinase domain mutations. Three patients progressed to the blastic phase. At a median follow-up of 84 (3-261) months, the 5-year EFS and OS for the entire cohort were 96.9% (95% CI: 93.4-100) and 98.7% (95% CI: 96.9-100) respectively. Screening for long-term toxicities revealed low bone density and hypovitaminosis D in 70% and 80% respectively. Other late effects included short stature (27%), delayed puberty (15%), poor sperm quality (43%) and miscellaneous endocrinopathies (8%). Children younger than 5 years at diagnosis were more susceptible to growth and endocrine toxicities (p = 0.009). Regular monitoring for long-term toxicities, timely intervention and trial of discontinuation whenever feasible are likely to improve the long-term outlook of pCML.

BCR/ABL-Positive Chronic Myeloid Leukemia in Children: Current Treatment Approach

PURPOSE OF REVIEW

The purpose of this review is to summarize the most updated treatment recommendations for pediatric CML, and to discuss current areas of investigation.

RECENT FINDINGS

There is new phase 1 data to support the safety of the non-ATP competitive tyrosine kinase inhibitor (TKI) asciminib in the pediatric cohort. Ongoing studies are investigating the role of treatment-free remission in children. Chronic phase CML in children is managed with lifelong TKI therapy; however, evidence of deeper remissions sustained with second-generation TKIs may permit shorter treatment courses. Use of more specific TKIs may mitigate some of the side effects specific to the pediatric cohort. Children with advanced phase CML should achieve a complete hematologic remission with use of a second-generation TKI prior to transplant to achieve the best outcome.

Skin reactions to tyrosine kinase inhibitors in pediatric patients with chronic myeloid leukemia

Cutaneous adverse events are commonly reported in adult patients with chronic myeloid leukemia (CML) receiving tyrosine kinase inhibitors (TKIs); however, little is known about the cutaneous reactions in children receiving TKIs for CML. As pediatric patients may require lifelong TKI therapy, it is essential to understand the wide range of potential cutaneous toxicities. We examined all case studies, cohort studies, and clinical trials in PubMed/MEDLINE and Embase that reported cutaneous reactions to first-, second-, and third-generation TKIs in children 18 years or younger with CML. This review article focuses on the TKI drug types and doses, patient demographic characteristics, features of skin reactions, and clinical outcomes.

Twenty years of evolution of CML therapy: how the treatment goal is moving from disease to patient

The introduction of imatinib in 2000 opened the era of tyrosine kinase inhibitors (TKIs) for CML therapy and has revolutionized the life expectancy of CML patients, which is now quite like the one of the healthy aged population. Over the last 20 years, both the TKI therapy itself and the objectives have undergone evolutions highlighted and discussed in this review. The main objective of the CML therapy in the first 10 years after TKI introduction was to abolish the disease progression from the chronic to the blastic phase and guarantee the long-term survival of the great majority of patients. In the second 10 years (from 2010 to the present), the main objective of CML therapy moved from survival, considered achieved as a goal, to treatment-free remission (TFR). Two phenomena emerged: no more than 50-60% of CML patients could be candidates for discontinuation and over 50% of them molecularly relapse. The increased cumulative incidence of specific TKI off-target side effects was such relevant to compel to discontinue or reduce the TKI administration in a significant proportion of patients and to avoid a specific TKI in particular settings of patients. Therefore, the treatment strategy must be adapted to each category of patients. What about the patients who do not get or fail the TFR? Should they be compelled to continue the TKIs at the maximum tolerated dose? Alternative strategies based on the principle of minimal effective dose have been tested with success and they are now re-evaluated with more attention, since they guarantee survival and probably a better quality of life, too. Moving from treating the disease to treating the patient is an important change of paradigm. We can say that we are entering a personalized CML therapy, which considers the patients' age, their comorbidities, tolerability, and specific objectives. In this scenario, the new techniques supporting the monitoring of the patients, such as the digital PCR, must be considered. In the present review, we present in deep this evolution and comment on the future perspectives of CML therapy.

Tyrosine Kinase Inhibitors in pediatric chronic myeloid leukemia: a focused review of clinical trials

Tyrosine Kinase Inhibitors (TKIs) is revolutionizing the management of pediatric Chronic Myeloid Leukemia (CML), offering alternatives to Allogeneic Hematopoietic Stem Cell Transplantation (AHSCT). We conducted a comprehensive review of 16 Randomized Controlled Trials (RCTs) encompassing 887 pediatric CML patients treated with TKIs including Imatinib, Dasatinib, and Nilotinib. The median patient age ranged from 6.5 to 14 years, with a median white blood cell count of 234 x 10^9/uL, median hemoglobin level of 9.05 g/dL, and median platelet count of 431.5 x 10^9/µL. Imatinib seems to be predominant first line TKI, with the most extensive safety and efficacy data. BCR::ABL response rates below 10% ranged from 60% to 78%, CCyR at 24 months ranged from 62% to 94%, and PFS showed variability from 56.8% to 100%, albeit with differing analysis timepoints. The Safety profile of TKIs was consistent with the known safety profile in adults. With the availability of three TKIs as first line options, multiple factors should be considered when selecting first line TKI, including drug formulation, administration, comorbidities, and financial issues. Careful monitoring of adverse events, especially in growing children, should be considered in long term follow-up clinical trials.

Continuous therapy response references for BCR::ABL1 monitoring in pediatric chronic myeloid leukemia

Response to tyrosine kinase inhibitor (TKI) therapy in patients with chronic myeloid leukemia (CML) is monitored by quantification of BCR::ABL1 transcript levels. Milestones for assessing optimal treatment response have been defined in adult CML patients and are applied to children and adolescents although it is questionable whether transferability to pediatric patients is appropriate regarding genetic and clinical differences. Therefore, we analyzed the molecular response kinetics to TKI therapy in 129 pediatric CML patients and investigated whether response assessment based on continuous references can support an early individual therapy adjustment. We applied a moving quantiles approach to establish a high-resolution response target curve and contrasted the median responses in all patients with the median of the ideal target curve obtained from a subgroup of optimal responders. The high-resolution response target curve of the optimal responder group presents a valuable tool for continuous therapy monitoring of individual pediatric CML patients in addition to the fixed milestones. By further comparing BCR::ABL1 transcript levels with BCR::ABL1 fusion gene copy numbers, it is also possible to model the differential dynamics of BCR::ABL1 expression and cell number under therapy. The developed methodology can be transferred to other biomarkers for continuous therapy monitoring.

The Recurrent Atypical e8a2 BCR::ABL1 Transcript with Insertion of an Inverted 55 Base Pair ABL1 Intron 1b Sequence: A Detailed Molecular Analysis

Atypical BCR::ABL1 transcripts are found in approximately 2% of cases of chronic myeloid leukemia. It is important to detect them since affected patients also benefit from tyrosine kinase inhibitor therapy. In the rare e8a2 atypical BCR::ABL1 transcript, two out-of-frame exons are fused, thus, interposed nucleotides are usually found at the fusion site to restore the reading frame. In approximately half of previously reported e8a2 BCR::ABL1 cases, an inserted 55 bp sequence homologous to an inverted sequence from ABL1 intron 1b was detected. The generation of this recurrent transcript variant is not obvious. This work describes the molecular analysis of such an e8a2 BCR::ABL1 translocation from a CML patient. The genomic chromosomal breakpoint is identified, and the formation of this transcript is theoretically explained. The clinical course of the patient is reported, and recommendations are provided for the molecular analysis of future e8a2 BCR::ABL1 cases.

Liquid biopsies and minimal residual disease in lymphoid malignancies

Minimal residual disease (MRD) assessment using peripheral blood instead of bone marrow aspirate/biopsy specimen or the biopsy of the cancerous infiltrated by lymphoid malignancies is an emerging technique with enormous interest of research and technological innovation at the current time. In some lymphoid malignancies (particularly ALL), Studies have shown that MRD monitoring of the peripheral blood may be an adequate alternative to frequent BM aspirations. However, additional studies investigating the biology of liquid biopsies in ALL and its potential as an MRD marker in larger patient cohorts in treatment protocols are warranted. Despite the promising data, there are still limitations in liquid biopsies in lymphoid malignancies, such as standardization of the sample collection and processing, determination of timing and duration for liquid biopsy analysis, and definition of the biological characteristics and specificity of the techniques evaluated such as flow cytometry, molecular techniques, and next generation sequencies. The use of liquid biopsy for detection of minimal residual disease in T-cell lymphoma is still experimental but it has made significant progress in multiple myeloma for example. Recent attempt to use artificial intelligence may help simplify the algorithm for testing and may help avoid inter-observer variation and operator dependency in these highly technically demanding testing process.

Digital PCR as a New Method for Minimal Residual Disease Monitoring and Treatment Free Remission Management in Chronic Myeloid Leukemia Patients: Is It Reliable?

The effective and sensitive monitoring of Minimal Residual Disease or Measurable Residual Disease (MRD) is a very important aspect in the management of patients affected by hematologic malignancies. The recent availability of new technologies has opened to the improvement of MRD monitoring. It is particularly relevant in patients affected by Chronic Myeloid Leukemia (CML). MRD monitoring is key in the management of CML patients thanks to the efficacy of TKIs therapy. Moreover, the policies of TKIs discontinuation aimed at treatment free remission are strongly based on the good selection of patients eligible for stopping TKIs therapy. The recently described application of digital PCR in CML patients monitoring seems to improve the accuracy and precision in the identification of optimal responders. The present review reports an overview on the application of digital PCR in the monitoring of MRD in CML and its impact on TKIs discontinuation trials and, consequently, on TFR success.

EAHP 2020 workshop proceedings, pediatric myeloid neoplasms

The first section of the bone marrow workshop of the European Association of Haematopathology (EAHP) 2020 Virtual Meeting was dedicated to pediatric myeloid neoplasms. The section covered the whole spectrum of myeloid neoplasms, including myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), myelodysplastic/myeloproliferative neoplasms (MDS/MPN), and acute myeloid leukemia (AML). The workshop cases are hereby presented, preceded by an introduction on these overall rare diseases in this age group. Very rare entities such as primary myelofibrosis, pediatric MDS with fibrosis, and MDS/MPN with JMML-like features and t(4;17)(q12;q21); FIP1L1::RARA fusion, are described in more detail.

The Cytogenetic Landscape of Pediatric Chronic Myeloid Leukemia Diagnosed in Chronic Phase

Simple Summary

Philadelphia chromosome-positive chronic myeloid leukemia (CML) is characterized by the translocation of the chromosomes 9 and 22. Additional non-Philadelphia aberrations of chromosomes (nPhAs) and their prognostic relevance for the disease course are comparably well known in adult patients with CML. However, due to the rarity of CML in children and adolescents, nPhAs have hardly been determined systematically in these age groups. Here, we present a large analysis of nPhAs detected in a cohort of 161 patients younger than 18 years who had been diagnosed with CML in chronic phase and enrolled in the German national CML-PAED-II registry. We found a distinct distribution of nPhAs in this pediatric cohort with possible impact on treatment response whereas the survival remained unaffected. Our findings emphasize differences in the disease biology between pediatric and adult patients and prompt further joint international efforts to acquire more data on the disease in this age group.

Abstract

Philadelphia chromosome-positive chronic myeloid leukemia (CML) is cytogenetically characterized by the classic translocation t(9;22)(q34;q11), whereas additional non-Philadelphia aberrations (nPhAs) have been studied extensively in adult patients with CML, knowledge on nPhAs in pediatric patients with CML is still sparse. Here, we have determined nPhAs in a cohort of 161 patients younger than 18 years diagnosed with chronic phase CML and consecutively enrolled in the German national CML-PAED-II registry. In 150 cases (93%), an informative cytogenetic analysis had been performed at diagnosis. In total, 21 individuals (13%) showed nPhAs. Of these, 12 (8%) had a variant translocation, 4 (3%) additional chromosomal aberrations (ACAs) and 5 (3%) harbored a complex karyotype. Chromosome 15 was recurrently involved in variant translocations. No significant impact of the cytogenetic subgroup on the time point of cytogenetic response was observed. Patients with a complex karyotype showed an inferior molecular response compared to patients carrying the classic translocation t(9;22)(q34;q11), variant translocations or ACAs. No significant differences in the probability of progression-free survival and overall survival was found between patients with nPhAs and patients with the classic Philadelphia translocation only. Our results highlight the distinct biology of pediatric CML and underline the need for joint international efforts to acquire more data on the disease pathogenesis in this age group.

Pediatric Myeloproliferative Neoplasms

Myeloproliferative neoplasms can present early in life and may present a diagnostic challenge. Very few studies have focused on the diagnosis, prognosis, and therapy for pediatric myeloproliferative neoplasms. This article focuses on chronic myeloid leukemia, essential thrombocythemia, polycythemia vera, and primary myelofibrosis in children.

Adolescents experienced more treatment failure than children with chronic myeloid leukemia receiving imatinib as frontline therapy: a retrospective multicenter study

To explore the differences in the clinical features, treatment responses, and outcomes among children, adolescents, and adults with chronic myeloid leukemia in the chronic phase (CML-CP) receiving imatinib as first-line therapy. Data from children (0-8 years for girls and 0-10 years for boys), adolescents (9-19 years for girls and 11-19 years for boys), and adults (age ≥ 20 years) with newly diagnosed CML-CP receiving imatinib as first-line therapy between 2006 and 2019 were retrospectively reviewed. In total, 135 children (cohort 1), 189 adolescents (cohort 2), and 658 adults (cohort 3: age 20-39 years, n = 305; cohort 4: age 40-59 years, n = 270; and cohort 5: age 60-83 years, n = 83) were included in this study. When compared with children, adolescents showed a significantly higher white blood cell count (P = 0.033) and basophil percentage in peripheral blood (P = 0.002) and a significantly higher prevalence of splenomegaly (P = 0.004). Both children and adolescents presented with more aggressive clinical features than adults. During median follow-ups of 28 months (range, 3-161 months) in children, 33 months (range, 3-152 months) in adolescents, and 48 months (range, 3-157 months) in adults, multivariate analysis showed that children and adolescents had higher probabilities of achieving complete cytogenetic response, major molecular response, and molecular response^4.5. Notably, compared with not only adults (cohort 3 vs. cohort 1: HR = 2.03 [1.03, 3.98], P = 0.040; cohort 4 vs. cohort 1: HR = 2.15 [1.07, 4.33], P = 0.033; cohort 5 vs. cohort 1: HR = 4.22 [1.94, 9.15], P < 0.001) but also adolescents (cohort 2 vs. cohort 1: HR = 2.36 [1.18, 4.72], P = 0.015), children had significantly longer failure-free survival. Age was not associated with progression-free survival or overall survival. Although they exhibited more aggressive clinical features at diagnosis, both children and adolescents achieved superior treatment responses than adults. Adolescents showed even more adverse features and a poor FFS than children.

VNTR polymorphism in the breakpoint region of ABL1 and susceptibility to bladder cancer

BACKGROUND

ABL1 is primarily known as a leukemia-related oncogene due to translocation, but about 2.2% of ABL1 mutations have been identified in bladder cancer, and high expression in solid cancer has also been detected.

METHODS

Here, we used the NCBI database, UCSC genome browser gateway and Tandem repeat finder program to investigate the structural characterization of the ABL1 breakpoint region and to identify the variable number of tandem repeats (VNTR). To investigate the relationship between ABL1-MS1 and bladder cancer, a case-controlled study was conducted in 207 controls and 197 bladder cancer patients. We also examined the level of transcription of the reporter gene driven by the ABL1 promoter to determine if the VNTR region affects gene expression.

RESULTS

In our study, one VNTR was identified in the breakpoint region, the intron 1 region of ABL1, and was named ABL1-MS1. In the control group, only two common alleles (TR13, TR15) were detected, but an additional two rare alleles (TR14, TR16) were detected in bladder cancer. A statistically significant association was identified between the rare ABL1-MS1 allele and bladder cancer risk: P = 0.013. Investigating the level of transcription of the reporter gene driven by the ABL1 promoter, VNTR showed inhibition of ABL1 expression in non-cancer cells 293 T, but not in bladder cancer cells. In addition, ABL1-MS1 was accurately passed on to offspring according to Mendelian inheritance through meiosis.

CONCLUSIONS

Therefore, the ABL1-MS1 region can affect ABL1 expression of bladder cancer. This study provides that ABL1-MS1 can be used as a DNA fingerprinting marker. In addition, rare allele detection can predict susceptibility to bladder cancer.

Tyrosine Kinase Inhibitors and Beyond for Chronic Myeloid Leukemia in Children

Chronic myeloid leukemia (CML) is rare in children but presents a unique challenge as recent drug innovations have turned CML into a chronic disease with implications for treatment into adulthood. With the approval of newer-generation tyrosine kinase inhibitors (TKIs) in addition to imatinib, providers have more options for the treatment of chronic-phase CML (CML-CP) in children. The second-generation TKIs approved for use in children, nilotinib and dasatinib, have higher response rates than first-generation imatinib; however, overall survival rates appear to be the same. Even more options may soon become available with ongoing investigations into the use of bosutinib and ponatinib and other new agents in children. Possible long-term side effects of TKIs, including growth failure, should be carefully acknowledged by the treating provider. Although these known associations may not preclude treatment, providers should be aware of them to guide their management of pediatric patients with CML being treated long term with TKI therapy. Treatment-free remission is a desired goal for pediatric patients and providers alike, but current recommendations are for attempts at achieving this to be restricted to clinical study settings.

Definition, Epidemiology, Pathophysiology, and Essential Criteria for Diagnosis of Pediatric Chronic Myeloid Leukemia

Simple Summary

The low incidence (1:1,000,000) of chronic myeloid leukemia (CML) in the first two decades of life presents an obstacle to accumulation of pediatric experience and knowledge on this leukemia. Biological features of CML are shared but also differing between adult and pediatric patients. This review aims; (i) to define the disease based on an unified terminology, (ii) to list the diseases to be considered as a differential diagnosis in children, (iii) to outlines the morphological, histopathological and immuno-phenotypical findings of pediatric CML, (iv) to illustrate rare but classical complications resulting from high white cell and platelet counts at diagnosis, and (v) to recommend a uniform approach for the diagnostic procedures to be applied. Evidently, only a clear detailed picture of all relevant features can lay the basis for standardized treatment approaches.

Abstract

Depending on the analytical tool applied, the hallmarks of chronic myeloid leukemia (CML) are the Philadelphia Chromosome and the resulting mRNA fusion transcript BCR-ABL1. With an incidence of 1 per 1 million of children this malignancy is very rare in the first 20 years of life. This article aims to; (i) define the disease based on the WHO nomenclature, the appropriate ICD 11 code and to unify the terminology, (ii) delineate features of epidemiology, etiology, and pathophysiology that are shared, but also differing between adult and pediatric patients with CML, (iii) give a short summary on the diseases to be considered as a differential diagnosis of pediatric CML, (iv) to describe the morphological, histopathological and immunophenotypical findings of CML in pediatric patients, (v) illustrate rare but classical complications resulting from rheological problems observed at diagnosis, (vi) list essential and desirable diagnostic criteria, which hopefully in the future will help to unify the attempts when approaching this rare pediatric malignancy.

Molecular Testing in CML between Old and New Methods: Are We at a Turning Point?

Molecular monitoring of minimal residual disease (MRD) and BCR-ABL1 kinase domain (KD) mutation testing have a well consolidated role in the routine management of chronic myeloid leukemia (CML) patients, as they provide precious information for therapeutic decision-making. Molecular response levels are used to define whether a patient has an "optimal", "warning", or "failure" response to tyrosine kinase inhibitor (TKI) therapy. Mutation status may be useful to decide whether TKI therapy should be changed and which alternative TKI (or TKIs) are most likely to be effective. Real-time quantitative polymerase chain reaction (RQ-qPCR) and Sanger sequencing are currently the gold standard for molecular response monitoring and mutation testing, respectively. However, in recent years, novel technologies such as digital PCR (dPCR) and next-generation sequencing (NGS) have been evaluated. Here, we critically describe the main features of these old and novel technologies, provide an overview of the recently published studies assessing the potential clinical value of dPCR and NGS, and discuss how the state of the art might evolve in the next years.

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.

Outcomes of children with chronic myeloid leukemia: A population-based cohort study

OBJECTIVE

Chronic myeloid leukemia (CML) is a rare disease in childhood. While hematopoietic stem cell transplant (HSCT) was the treatment of choice for CML prior to 2000, the introduction of tyrosine kinase inhibitors (TKIs) changed the management of this disease. This population-based analysis was conducted in the province of Ontario, Canada to gather information on treatment choices and outcomes of childhood CML.

METHOD

Using a provincial childhood cancer registry and retrospective review of patient medical records for patients < 18 years diagnosed with CML between 1985 and 2018, data on presenting features, treatment, and outcomes were collected from 52 patients.

RESULTS

Patients treated before the introduction of TKIs (before 2002) mainly received HSCT and had an overall survival (OS) of 64% at a median follow up of 6 years. The OS of all patients treated in the TKI era (2002 and after) was 90% at a median follow up of 3 years. All three deaths in the TKI era were related to HSCT complications. Survival of patients who remained on a TKI was significantly improved compared to those who underwent HSCT post-TKI therapy (100% vs 66%, P = .008). TKIs were well tolerated.

CONCLUSION

Given the increased mortality associated with HSCT in our cohort, further advances in HSCT may be required to outweigh the benefits of a TKI monotherapy approach in the majority of childhood CML patients. We believe HSCT should be considered in only a limited subset of pediatric patients with CML.

Real-world Experience of Imatinib in Pediatric Chronic Phase Chronic Myeloid Leukemia: A Single-center Experience From India

INTRODUCTION

Chronic myeloid leukemia (CML) is an uncommon malignancy in children in which tyrosine kinase inhibitors (TKIs) have significantly improved outcome in recent years.

PATIENTS AND METHODS

We performed a retrospective analysis of CML patients (≤ 18 years old) presenting to our center between January 2005 and December 2018 with respect to baseline demographics, response to imatinib, and real-world management of those with a suboptimal response.

RESULTS

A total of 124 patients were diagnosed with CML with 99 (80%) in the chronic phase. There was a male preponderance (males:females = 3.1:1) with a median age of 13 years. The common presenting clinical features were splenomegaly (90.9%) and fever (51.5%) with a median leukocyte count of 165 × 103/μL. The proportion of patients attaining a complete hematologic response (CHR) at 3 months, a complete cytogenetic response (CCyR) at 12 months, and a major molecular response at 12 months were 79.7%, 54.1%, and 50.9%, respectively. At a median follow-up of 67.4 months, the 5-year overall survival rate and the event-free survival (EFS) rate were 92% ± 3% and 64% ± 6%, respectively. Failure to achieve CCyR at 12 months was associated with poor EFS beyond 1 year (hazard ratio = 2.865, P = .044). Among 15 patients not achieving CHR at 3 months, dose escalation of imatinib resulted in the attainment of CHR in 13 (87%) patients. Seven patients in the cohort had a loss of the established response to imatinib because of documented poor compliance.

CONCLUSION

Imatinib remains the frontline treatment of choice in CML with a reasonable outcome in children, especially when financial affordability, availability of second-generation TKIs, and poor compliance still remain major challenges in management. Dose escalation of imatinib remains an option in patients with a suboptimal response.

Horn of plenty: Value of the international registry for pediatric chronic myeloid leukemia

Chronic myeloid leukemia (CML) in minors is a rare disease which can be effectively treated by tyrosine kinase inhibitors (TKIs) since the year 2000. A majority of pediatricians will encounter one or two CML patients in the course of their careers and will typically have to rely on written information along with their own intuition to provide care. Knowledge of response to TKIs and of age-specific side effects has an impact on the design of pediatric CML trials in many ways aiming to contribute toward greater predictability of clinical improvements. Information from a registry on a rare disease like CML offers the enormous benefit of enabling treating physicians to interact and share their collective experience. The International Registry on Pediatric CML (IR-PCML) was founded at Poitiers/France almost 10 years ago. Since then, the number of collaboration centers and in parallel of registered patients continuously increased (> 550 patients as of December 2019). Ideally, from a given treatment center in a country data are transferred to a national coordinator who interacts with the IR-PCML. In the sense of quality assurance, the registry can offer dissemination of knowledge on state-of-the-art diagnostics (including reference appraisal), optimal treatment approaches, and follow-up procedures within a network that is exerting its strength via participation. With continuous growth during the recent years, very rare subgroups of patients could be identified (e.g., CML diagnosed at age < 3 years, children presenting with specific problems at diagnosis or during course of treatment) which had not been described before. Publications coming from the IR-PCML disseminated this useful information derived from patients who robustly participate and share information about their disease, among themselves and with their caregivers and clinicians. Patient input driving the collection of data on this rare leukemia is the basis for the considerable success of bringing new therapeutics into clinical use.

Chronic Myeloid Leukemia in Children: Challenges and Opportunities : Based on 7th Dr. I. C. Verma Excellence Award for Young Pediatricians Delivered as Oration on 29th Sept. 2019

Treatment with tyrosine kinase inhibitors (TKI) is an effective therapy for children and adolescents with chronic phase of chronic myeloid leukemia (CML). For the majority of patients with CML in low- and middle-income countries (LMIC), imatinib is the TKI of choice for reasons of cost, availability, and experience. Children are exposed to therapy for a greater proportion of their lifetime as compared to adults. The adverse effects of prolonged administration of TKI is a subject of ongoing research, as more experience is collected. Therapy with TKI is currently considered to be life-long. Trials on stopping treatment are ongoing to explore if it may be feasible in selected patients, as reported in adults. Growth-failure is a concerning adverse effect. Currently, it seems unclear if the final height attained is within the expected range of the mid-parenteral height and growth standards. Whether the children will achieve a normal height at the end of their growth potential or remain below the predicted range is critical to decide if therapeutic interventions (E.g., growth hormone therapy, or interruption in TKI) should be considered during the period of growth potential. Research on CML in children is at a relatively slow pace, largely due to the rarity of the disease. This provides a unique opportunity for research in population-dense LMICs, as several tertiary centers tend to have a sizable cohort of children and adolescents with CML on follow-up. This narrative summarises the challenges and opportunities in dealing with CML in children, particularly in reference to a center in LMIC.

Monitoring of Minimal Residual Disease (MRD) in Chronic Myeloid Leukemia: Recent Advances

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm caused by the BCR-ABL1 fusion gene generation as a consequence of the t(9;22)(q34;q11) rearrangement. The identification of the BCR-ABL1 transcript was of critical importance for both CML diagnosis and minimal residual disease (MRD) monitoring. In this review, we report the recent advances in the CML MRD monitoring based on RNA, DNA and protein analysis. The detection of the BCR-ABL1 transcript by the quantitative reverse-transcriptase polymerase chain reaction is the gold standard method, but other systems based on digital PCR or on GeneXpert technology have been developed. In the last years, DNA-based assays showed high sensitivity and specificity, and flow cytometric approaches for the detection of the BCR-ABL1 fusion protein have also been tested. Recently, new MRD monitoring systems based on the detection of molecular markers other than the BCR-ABL1 fusion were proposed. These approaches, such as the identification of CD26+ leukemic stem cells, microRNAs and mitochondrial DNA mutations, just remain preliminary and need to be implemented. In the precision medicine era, the constant improvement of the CML MRD monitoring practice could allow clinicians to choose the best therapeutic algorithm and a more accurate selection of CML patients eligible for the tyrosine kinase inhibitors discontinuation.

Molecular Composition of Genomic TMPRSS2-ERG Rearrangements in Prostate Cancer

There is increasing interest in the use of cell-free circulating tumor DNA (ctDNA) as a serum marker for therapy assessment in prostate cancer patients. Prostate cancer is characterized by relatively low numbers of mutations, and, in contrast to many other common epithelial cancers, commercially available single nucleotide mutation assays for quantification of ctDNA are insufficient for therapy assessment in this disease. However, prostate cancer shares some similarity with translocation-affected mesenchymal tumors (e.g., leukemia and Ewing sarcoma), which are common in pediatric oncology, where chromosomal translocations are used as biomarkers for quantification of the tumor burden. Approximately 50% of prostate cancers carry a chromosomal translocation resulting in generation of the TMPRSS2-ERG fusion gene, which is unique to the tumor cells of each individual patient because of variability in the fusion breakpoint sites. In the present study, we examined the structural preconditions for TMPRSS2-ERG fusion sites in comparison with mesenchymal tumors in pediatric patients to determine whether the sequence composition is suitable for the establishment of tumor-specific quantification assays in prostate cancer patients. Genomic repeat elements represent potential obstacles to establishment of quantification assays, and we found similar proportions of repeat elements at fusion sites in prostate cancer to those reported for mesenchymal tumors, where genomic fusion sequences are established as biomarkers. Our data support the development of the TMPRSS2-ERG fusion gene as a noninvasive tumor marker for therapy assessment, risk stratification, and relapse detection to improve personalized therapy strategies for patients with prostate cancer.

Management of chronic myeloid leukemia in children and adolescents: Recommendations from the Children's Oncology Group CML Working Group

Chronic myeloid leukemia (CML) accounts for 2-3% of leukemias in children under 15 and 9% in adolescents aged 15-19. The diagnosis and management of CML in children, adolescents, and young adults have several differences compared to that in adults. This review outlines the diagnosis and management of the underlying disease as well as challenges that can occur when dealing with CML in this patient population.

Paediatric chronic myeloid leukaemia: Is it really a different disease?

Paediatric chronic myeloid leukaemia (CML) has biological and clinical differences from adult CML. Management of paediatric CML presents unique challenges in growing children, and there are no specific guidelines for paediatric CML. This review focusses on the clinical characteristics, diagnostic issues and management of paediatric CML. Major studies that provide the basis of managing paediatric CML are summerized here. Studies conducted on adult CML patients were used to guide the management of places where studies were lacking in paediatric CML. Recently, dasatinib and nilotinib have been approved for treatment of paediatric CML, and their role has been discussed in the current management perspective. Allogeneic transplant, fertility and vaccination in paediatric CML, have also been discussed.

Large amplicon droplet digital PCR for DNA-based monitoring of pediatric chronic myeloid leukaemia

Quantification of tumour‐specific molecular markers at the RNA and DNA level for treatment response monitoring is crucial for risk‐adapted stratification and guidance of individualized therapy in leukaemia and other malignancies. Most pediatric leukaemias and solid tumours of mesenchymal origin are characterized by a relatively low mutation burden at the single nucleotide level and the presence of recurrent chromosomal translocations. The genomic fusion sites resulting from translocations are stable molecular tumour markers; however, repeat‐rich DNA sequences flanking intronic breakpoints limit the design of high sensitivity PCR assays for minimal residual disease (MRD) monitoring. Here, we quantitatively evaluated the impact of repeat elements on assay selection and the feasibility of using extended amplicons (≤1330 bp) amplified by droplet digital PCR to monitor pediatric chronic myeloid leukaemia (CML). Molecular characterization of 178 genomic BCR‐ABL1 fusion sites showed that 64% were located within sequence repeat elements, impeding optimal primer/probe design. Comparative quantification of DNA and RNA BCR‐ABL1 copy numbers in 687 specimens from 55 pediatric patients revealed that their levels were highly correlated. The combination of droplet digital PCR, double quenched probes and extended amplicons represents a valuable tool for sensitive MRD assessment in CML and may be adapted to other translocation‐positive tumours.

IKZF1 deletion and co-occurrence with other aberrations in a child with chronic myeloid leukemia progressing to acute lymphoblastic leukemia

Chronic myeloid leukemia (CML) is a rare disease in children. Different from that in adults, childhood CML involves transformative events occurring over a short time period. CML transformation to lymphoid blast phase (BP) is associated with copy number abnormalities, characteristic of BCR-ABL1 positive acute lymphoblastic leukemia, but not of CML in the chronic phase. Here, we present an unusual case of CML progressing to BP in a 1.6-year-old child, harboring IKZF1, PAX5, CDKN2A, and ETV6 deletions at diagnosis. It remains to be addressed whether distinct mechanisms might account for CML pathogenesis in early childhood.

How I treat chronic myeloid leukemia in children and adolescents

Evidence-based recommendations have been established for treatment of chronic myeloid leukemia (CML) in adults treated with tyrosine kinase inhibitors (TKIs), but the rarity of this leukemia in children and adolescents makes it challenging to develop similar recommendations in pediatrics. In addition to imatinib, which was approved for pediatric CML in 2003, the second-generation TKIs dasatinib and nilotinib were recently approved for use in children, expanding the therapeutic options and pushing allogeneic stem cell transplantation to a third-line treatment of most pediatric cases. Yet, without sufficient data on efficacy and safety specific to pediatric patients, the selection of a TKI continues to rely on clinical experience in adults. Here, we present 4 case scenarios highlighting common yet challenging issues encountered in the treatment of pediatric CML (suboptimal response, poor treatment adherence, growth retardation, and presentation in advanced phases). Limited experience with very young children, the transition of teenagers to adult medicine, and the goal of achieving treatment-free remission for this rare leukemia are additional significant obstacles that require further clinical investigation through international collaboration.

Discontinuation of imatinib in children with chronic myeloid leukaemia in sustained deep molecular remission: results of the STOP IMAPED study

This international study aimed to assess the effect of imatinib discontinuation in paediatric patients with chronic myeloid leukaemia (CML) after deep molecular remission (DMR) had been achieved and maintained for at least 2 years. The primary endpoint of this analysis was the molecular relapse-free survival, estimated by the non-parametric Kaplan-Meier method. Major endpoint was the estimated rate of patients without molecular relapse at 6 months. Fourteen patients were enrolled; 4 patients maintained DMR with a follow-up of 24 (two patients), 34 and 66 months, respectively, whereas 10 patients relapsed. All molecular relapses occurred within 6 months (median 3 months, range 1-6) after imatinib discontinuation. The overall probability of maintaining DMR at 6 months was 28·6%. No parameters associated with molecular relapse could be identified. Keeping in mind the rarity of paediatric CML, which contributed to the small size of the cohort, our findings illustrate that imatinib cessation after sustained DMR is successful in only limited numbers of patients, whereas much higher rates are reported in adult patients. Further research is needed to extend the cohort of paediatric CML patients who might achieve treatment-free remission with an ideal prerequisite of predicting the occurrence of molecular relapse l after imatinib cessation.

Characterization and diagnostic application of genomic NPM-ALK fusion sequences in anaplastic large-cell lymphoma

Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) fusion genes resulting from the translocation t(2;5)(p23;q35) are present in almost 90% of childhood ALK-positive anaplastic large-cell lymphomas (ALCL). Detection and quantification of minimal disseminated disease (MDD) by measuring NPM-ALK fusion transcript levels in the blood provide independent prognostic parameters. Characterization of the genomic breakpoints provides insights into the pathogenesis of the translocation and allows for DNA-based minimal disease monitoring.

We designed a nested multiplex PCR assay for identification and characterization of genomic NPM-ALK fusion sequences in 45 pediatric ALCL-patients, and used the sequences for quantitative MDD monitoring. Breakpoint analysis indicates the involvement of inaccurate non-homologous end joining repair mechanisms in the formation of NPM-ALK fusions. Parallel quantification of RNA and DNA levels in the cellular fraction of 45 blood samples from eight patients with NPM-ALK-positive ALCL correlated, as did cell-free circulating NPM-ALK DNA copies in the plasma fraction of 37 blood samples. With genomic NPM-ALK fusion sequence quantification, plasma samples of ALCL patients become an additional source for MRD-assessment. Parallel quantification of NPM-ALK transcripts and fusion genes in ALCL cell lines treated with the ALK kinase inhibitor crizotinib illustrates the potential value of supplementary DNA-based quantification in particular clinical settings.

A Rare Case of Pediatric Chronic Myelogenous Leukemia Presenting With Severe Thrombocytosis Without Leukocytosis

Pediatric chronic myelogenous leukemia is uncommon. We report a pediatric patient with chronic myelogenous leukemia presenting with a normal white blood cell count and no circulating immature myeloid cells. The patient presented with extreme thrombocytosis (platelet count range: 2175-3064 × 10⁹/L) noted incidentally. No splenomegaly was found. Examination of the bone marrow aspirate revealed normal cellularity and normal myeloid: erythroid ratio with marked megakaryocytic hyperplasia. Molecular studies on the bone marrow aspirate detected both the major BCR/ABL1 p210 fusion transcript (9280 copies; p210/ ABL1 ratio: 38.2%) and the minor p190 transcript (below limit of quantitation). The platelet count normalized within 2 weeks after treatment with the second-generation tyrosine kinase inhibitor dasatinib. Follow-up after 3 months revealed a 1.87 log reduction in p210 transcripts compared to diagnosis and no detectable p190 transcripts. This case highlights the need to include BCR/ABL1 fusion testing to accurately diagnose pediatric patients presenting with isolated thrombocytosis.

Monitoring of childhood ALL using BCR-ABL1 genomic breakpoints identifies a subgroup with CML-like biology

We used the genomic breakpoint between BCR and ABL1 genes for the DNA-based monitoring of minimal residual disease (MRD) in 48 patients with childhood acute lymphoblastic leukemia (ALL). Comparing the results with standard MRD monitoring based on immunoglobulin/T-cell receptor (Ig/TCR) gene rearrangements and with quantification of IKZF1 deletion, we observed very good correlation for the methods in a majority of patients; however, >20% of children (25% [8/32] with minor and 12.5% [1/8] with major-BCR-ABL1 variants in the consecutive cohorts) had significantly (>1 log) higher levels of BCR-ABL1 fusion than Ig/TCR rearrangements and/or IKZF1 deletion. We performed cell sorting of the diagnostic material and assessed the frequency of BCR-ABL1-positive cells in various hematopoietic subpopulations; 12% to 83% of non-ALL B lymphocytes, T cells, and/or myeloid cells harbored the BCR-ABL1 fusion in patients with discrepant MRD results. The multilineage involvement of the BCR-ABL1-positive clone demonstrates that in some patients diagnosed with BCR-ABL1-positive ALL, a multipotent hematopoietic progenitor is affected by the BCR-ABL1 fusion. These patients have BCR-ABL1-positive clonal hematopoiesis resembling a chronic myeloid leukemia (CML)-like disease manifesting in "lymphoid blast crisis." The biological heterogeneity of BCR-ABL1-positive ALL may impact the patient outcomes and optimal treatment (early stem cell transplantation vs long-term administration of tyrosine-kinase inhibitors) as well as on MRD testing. Therefore, we recommend further investigations on CML-like BCR-ABL1-positive ALL.

Optimal management for pediatric chronic myeloid leukemia

Chronic myeloid leukemia (CML) is rare among childhood leukemias. Its incidence increases with age, from 0.09/100 000 at ≤15 years old to 7.88/100 000 at ≥75 years old. There are several biological and clinical differences between pediatric and adult CML. Markedly increased leukocyte count and a higher incidence of splenomegaly are characteristic features at diagnosis in pediatric patients. The therapeutic approach to CML has changed since the introduction of the tyrosine kinase inhibitor (TKI) imatinib, followed by dasatinib and nilotinib. Given the efficacy of TKI in adult CML, TKI are regarded as the established first-line treatment in adult patients. In 2011, a prospective phase IV study in pediatric patients showed the excellent efficacy and safety of imatinib. Imatinib is also accepted as a first-line option for childhood chronic phase CML. Although the efficacy of dasatinib and nilotinib reported in adult studies seems very attractive for pediatric patients, neither drug has been prospectively investigated in a large pediatric cohort. TKI are designed to inhibit BCR-ABL1 kinase, but they have unfavorable effects, so-called "off-target" complications, such as growth impairment. Long-term morbidity due to TKI is unknown. Furthermore, the adverse effects on growing children have not been clearly elucidated, even though the exposure period to imatinib is relatively short. To establish the standard therapeutic management for pediatric CML, it is important to prospectively confirm the attractive outcomes obtained in adult studies via pediatric clinical trials with a careful monitoring system for TKI-induced adverse effects, especially in growing children.

Pediatric chronic myeloid leukemia is a unique disease that requires a different approach

Chronic myelogenous leukemia (CML) in children is relatively rare. Because of a lack of robust clinical study evidence, management of CML in children is not standardized and often follows guidelines developed for adults. Children and young adults tend to have a more aggressive clinical presentation than older adults, and prognostic scores for adult CML do not apply to children. CML in children has been considered to have the same biology as in adults, but recent data indicate that some genetic differences exist in pediatric and adult CML. Because children with CML may receive tyrosine kinase inhibitor (TKI) therapy for many decades, and are exposed to TKIs during a period of active growth, morbidities in children with CML may be distinct from those in adults and require careful monitoring. Aggressive strategies, such as eradication of CML stem cells with limited duration and intensive regimens of chemotherapy and TKIs, may be more advantageous in children as a way to avoid lifelong exposure to TKIs and their associated adverse effects. Blood and marrow transplantation in pediatric CML is currently indicated only for recurrent progressive disease, and the acute and long-term toxicities of this option should be carefully evaluated against the complications associated with lifelong use of TKIs.

Characterization of 46 patient-specific BCR-ABL1 fusions and detection of SNPs upstream and downstream the breakpoints in chronic myeloid leukemia using next generation sequencing

In chronic myeloid leukemia, the identification of individual BCR-ABL1 fusions is required for the development of personalized medicine approach for minimal residual disease monitoring at the DNA level. Next generation sequencing (NGS) of amplicons larger than 1000 bp simplified and accelerated a process of characterization of patient-specific BCR-ABL1 genomic fusions. NGS of large regions upstream and downstream the individual breakpoints in BCR and ABL1 genes, respectively, also provided information about the sequence variants such are single nucleotide polymorphisms.

Chronic myeloid leukemia in children: clinical findings, management, and unanswered questions

Chronic myelogenous leukemia (CML) is a rare disease in children. There is little evidence of biological differences between CML in children and adults, although host factors are different. Children develop distinct morbidities related to the off-target effects of tyrosine kinase inhibitors. The goal of treatment in children should be cure rather than suppression of disease, which can be the treatment goal for many older adults. This article reviews data from the literature on the treatment of CML, discusses the issues that are unique to CML in children, and recommends management that takes these issues into consideration.

Sustained complete molecular remission after imatinib discontinuation in children with chronic myeloid leukemia

Approximately 40% of adults with chronic myeloid leukemia (CML) in prolonged complete molecular response (CMR) remain in CMR after imatinib discontinuation. Corresponding information in children is lacking. Two children with CML in CMR for 48 and 19 months after imatinib discontinuation showed low-level fluctuating disease at RNA transcript and genomic DNA levels. Both patients were low risk according to adult criteria. Since adults with molecular relapse responded to re-introduction of imatinib, we postulated that treatment discontinuation in low risk children might be justified within clinical trials with close monitoring. This may help to minimize exposure to imatinib and its potential side effects.

Managing children with chronic myeloid leukaemia (CML): recommendations for the management of CML in children and young people up to the age of 18 years

Chronic myeloid leukaemia in children and young people is a relatively rare form of leukaemia that shows increased incidence with age and some evidence suggests that the molecular basis differs from that in adults. Significant advances in targeted therapy with the development and use in children of tyrosine kinase inhibitors and the ability to monitor and understand the prognostic significance of minimal residual disease by standardized molecular techniques has shifted the management of this condition from bone marrow transplantation as the main therapeutic modality to individualized treatment for each patient based on achieving specific milestones. The physiological changes occurring during childhood, particularly those affecting growth and development and the long-term use of treatment, pose specific challenges in this age group, which we are only beginning to understand.

Identification of the genomic BCR-ABL1 fusion sequence from blood specimen stored on filter paper

Chronic myeloid leukaemia (CML) is characterized by the Philadelphia chromosome resulting in the BCR-ABL1 gene whose mRNA transcript detection is commonly used for diagnosis and monitoring of therapeutic response. However, in collected blood specimen degradation of mRNA has to be considered during storage and transport thus jeopardizing the analysis. We here describe an alternative DNA-based technique applied after long-term blood storage. DNA was isolated from dried blood stains from CML patients stored on filter paper (Guthrie cards) after a median period from diagnosis of 11 years (range: 5-12 years) and analyzed with a two round long-range multiplex PCR (MLR-PCR) to identify the genomic BCR-ABL1 breakpoint. Patient-specific individual BCR-ABL1 fusion sites were successfully detected in 10 out of 13 patients. Dried blood stains represent a valuable resource for genomic DNA analyses. Long term preservation is easily manageable in paper envelopes with the patient's medical files with a minimum of financial costs and efforts. Such the cooperation between laboratories and hospitals separated by long distances is facilitated rendering possible offering specialized genomic analyses to patients with CML virtually everywhere around the world. This technique may also be a valuable approach for diagnostic procedures on a high molecular level in related haematological malignancies.