DNA Index in childhood acute lymphoblastic leukaemia: a karyotypic method to validate the flow cytometric measurement

Distinct Immunophenotypes in the DNA Index-Based Stratification of Pediatric B-Cell Acute Lymphoblastic Leukemia

BACKGROUND/OBJECTIVES

B-cell acute lymphoblastic leukemia (B-ALL) presents a challenge in hematological malignancies due to its heterogeneity, which impacts treatment outcomes. Stratification based on the DNA index (DNAi) categorizes patients into favorable prognosis (hyperploid), standard prognosis (normoploid), and uncertain or poor prognosis (hypoploid) groups. In this study, we explored whether specific immunophenotypic markers are associated with each DNAi-based group and their potential connection to prognostic categories, aiming to provide new insights that may contribute to a better understanding of prognosis in B-ALL.

METHODS

In this study, we utilized flow cytometry to analyze immunophenotypic markers and combined this with DNA index (DNAi) measurements to stratify pediatric B-ALL patients into distinct risk categories. Our methodology focused on accurately classifying patients into hyperploid, normoploid, and hypoploid groups based on their DNA content, facilitating a comparative analysis of immunophenotypic characteristics across these groups.

RESULTS

Our analysis revealed that hypoploid B-ALL patients displayed a significantly lower percentage of cells in the S phase of the cell cycle compared to normoploid and hyperploid groups. Additionally, distinct immunophenotypic profiles were observed in hypoploid patients, characterized by higher expression levels of HLA-DR and a notable co-expression of CD34 and CD22.

CONCLUSIONS

This study found that hypoploid B-ALL patients have distinct characteristics, such as lower S-phase cell percentages and specific immunophenotypic profiles, including higher HLA-DR expression and CD34/CD22 co-expression. These differences across DNA index-based prognostic categories warrant further research to explore their potential prognostic significance.

Prognostic and Pharmacotypic Heterogeneity of Hyperdiploidy in Childhood ALL

PURPOSE

High hyperdiploidy, the largest and favorable subtype of childhood ALL, exhibits significant biological and prognostic heterogeneity. However, factors contributing to the varied treatment response and the optimal definition of hyperdiploidy remain uncertain.

METHODS

We analyzed outcomes of patients treated on two consecutive frontline ALL protocols, using six different definitions of hyperdiploidy: chromosome number 51-67 (Chr51-67); DNA index (DI; DI1.16-1.6); United Kingdom ALL study group low-risk hyperdiploid, either trisomy of chromosomes 17 and 18 or +17 or +18 in the absence of +5 and +20; single trisomy of chromosome 18; double trisomy of chromosomes 4 and 10; and triple trisomy (TT) of chromosomes 4, 10, and 17. Additionally, we characterized ALL ex vivo pharmacotypes across eight main cytotoxic drugs.

RESULTS

Among 1,096 patients analyzed, 915 had B-ALL and 634 had pharmacotyping performed. In univariate analysis, TT emerged as the most favorable criterion for event-free survival (EFS; 10-year EFS, 97.3% v 86.8%; P = .0003) and cumulative incidence of relapse (CIR; 10-year CIR, 1.4% v 8.8%; P = .002) compared with the remaining B-ALL. In multivariable analysis, accounting for patient numbers using the akaike information criterion (AIC), DI1.16-1.6 was the most favorable criterion, exhibiting the best AIC for both EFS (hazard ratio [HR], 0.45; 95% CI, 0.23 to 0.88) and CIR (HR, 0.45; 95% CI, 0.21 to 0.99). Hyperdiploidy and subgroups with favorable prognoses exhibited notable sensitivities to asparaginase and mercaptopurine. Specifically, asparaginase sensitivity was associated with trisomy of chromosomes 16 and 17, whereas mercaptopurine sensitivity was linked to gains of chromosomes 14 and 17.

CONCLUSION

Among different definitions of hyperdiploid ALL, DI is optimal based on independent prognostic impact and also the large proportion of low-risk patients identified. Hyperdiploid ALL exhibited particular sensitivities to asparaginase and mercaptopurine, with chromosome-specific associations.

Diagnostic Accuracy of Flow Cytometric DNA Index in Saudi Children with B Cell Acute Lymphoblastic Leukemia

B cell Acute Lymphoblastic Leukemia (B-ALL) is one of the most common types of cancer diagnosed in children in Saudi Arabia. Cytogenetic investigations, including karyotyping and FISH, are used to determine the incidence and prognostic significance of chromosomal abnormalities in B-ALL. However, in ALL, accurate identification of the morphology of chromosomes is sometimes not achieved. Flow cytometric DI may have the advantage of being technically fast, using either fresh or frozen samples to correctly stratify the patient into the appropriate risk group for treatment. In this study, we evaluated the reliability and validity of using fixed samples instead of fresh samples to determine aneuploidy in cancer cells using a DNA index. The results of the DNA index obtained by flow cytometry were compared with those of conventional cytogenetic analysis to validate the accuracy. Fixed samples (n = 72) from children diagnosed with B-ALL at King Fahad Medical City in Riyadh between 2017 and 2019 were investigated. The results showed strong and statistically significant positive correlation between DNAI-FCM and conventional cytogenetic analysis (p = 0.000 < 0.01). The DNA index value by flow cytometry was proportional to the cytogenetic study in 94.36% (67) of the cases, while discrepancy was observed in 5.6% (four) cases. Our findings highlight the ability of the DNA index method to provide complementary information for the accurate diagnosis of aneuploidy in patients with B-ALL.

Hyperdiploidy: the longest known, most prevalent, and most enigmatic form of acute lymphoblastic leukemia in children

Hyperdiploidy is the largest genetic entity B-cell precursor acute lymphoblastic leukemia in children. The diagnostic hallmark of its two variants that will be discussed in detail herein is a chromosome count between 52 and 67, respectively. The classical HD form consists of heterozygous di-, tri-, and tetrasomies, whereas the nonclassical one (usually viewed as "duplicated hyperhaploid") contains only disomies and tetrasomies. Despite their apparently different clinical behavior, we show that these two sub-forms can in principle be produced by the same chromosomal maldistribution mechanism. Moreover, their respective array, gene expression, and mutation patterns also indicate that they are biologically more similar than hitherto appreciated. Even though in-depth analyses of the genomic intricacies of classical HD leukemias are indispensable for the elucidation of the disease process, the ensuing results play at present surprisingly little role in treatment stratification, a fact that can be attributed to the overall good prognoses and low relapse rates of the concerned patients and, consequently, their excellent treatment outcome. Irrespective of this underutilization, however, the detailed genetic characterization of HD leukemias may, especially in planned treatment reduction trials, eventually become important for further treatment stratification, patient management, and the clinical elucidation of outcome data. It should therefore become an integral part of all upcoming treatment studies.

Detecting hypodiploidy with endoreduplication and masked hypodiploidy in B-cell acute lymphoblastic leukemia using multicolor flow cytometry

BACKGROUND

Multicolor flow cytometry-based DNA-ploidy (MFC-ploidy) analysis is a simple, sensitive, and popular method for ploidy analysis in B-cell acute lymphoblastic leukemia (B-ALL). However, the utility of MFC-ploidy in the detection of B-ALL with endoreduplication or masked hypodiploidy has not been reported. Herein, we studied the patterns of MFC-ploidy assessment and its utility to detect B-ALL with hypodiploidy and endoreduplication.

METHODS

MFC-ploidy analysis was performed using FxCycle Violet-dye-based method, and cytogenetic ploidy was evaluated using chromosomal-counting and FISH analysis. A total of 20 B-ALL cases with endoreduplication were studied for the patterns of MFC-ploidy analysis and compared with 250 patients with hyperdiploidy and 11 cases with pure hypodiploidy.

RESULTS

All B-ALL with endoreduplication revealed two distinct peaks (populations) on MFC-ploidy analysis: the first (hypodiploid) peak (median-DNA-index [DI], 0.82; range, 0.6-0.95) and the second (hyperdiploid) peak with almost twice DI (median-DI, 1.53; range, 1.14-1.75). Cytogenetic findings were available in 19 cases and confirmed hypodiploidy with endoreduplication in 13/19 (68.4%) and only hypodiploidy in 3/19 cases. The remaining three cases showed hyperdiploid blasts in cytogenetic studies. Of these three, two cases had <10% blasts population with hypodiploidy. Thus, masked-hypodiploidy could be diagnosed correctly in 3/19 cases on MFC-ploidy analysis.

CONCLUSION

MFC-ploidy analysis shows a characteristic pattern of DNA-ploidy in samples with endoreduplication. It allows the distinction between samples with masked hypodiploidy from true hyperdiploidy. An integrated approach involving cytogenetic and MFC-ploidy detection is very helpful in the risk stratification of B-ALL in routine clinical practice.

Genetic and immunophenotypic diversity of acute leukemias in children

Acute leukemias are the most commonly diagnosed malignancies in children. Acute leukemias constitute a heterogeneous group of cancers resulting from clonal outgrowth and accumulation of immature precursor cells of different hematologic lineages. Cancerous transformation begins with disruption of cell maturation mechanisms triggered by particular environmental or endogenic factors, including innate and acquired immunodeficiencies as well as autoimmune diseases.

Research in the field of acute leukemias has revealed many possible genetic abnormalities in leukemic cells, including both structural and numerical aberrations. The former can produce some particular fusion genes, yielding fusion protein products which can have an oncogenic potential in hematopoietic cells. Some of them, including translocations resulting in fusion product formation BCR-ABL1 and different fusion products involving the KMT2A gene, are markers of adverse prognosis, whereas numerical aberrations with high hyperdiploidy and chromosome number exceeding 51 are markers of favorable prognosis. Detection of these aberrations already has a well-grounded clinical significance in acute lymphoblastic leukemia and plays an important role in patient risk stratification. The appearance of particular genetic changes often correlates with the expression of certain markers on the surface of leukemic cells. Determination of expression or lack of specific antigens, that is, immunophenotyping, is possible with the use of the flow cytometry technique. Flow cytometry is currently considered as a fast and broadly available technique which can provide clinically useful information in a relatively short time after biological specimen collection. Flow cytometry also enables appropriate classification of acute leukemias.

Cytogenetic Characteristics of Childhood Acute Lymphoblastic Leukemia: A Study of 1541 Chinese Patients Newly Diagnosed between 2001 and 2014

OBJECTIVE

Cytogenetic abnormalities have been proven to be the most valuable parameter for risk stratification of childhood acute lymphoblastic leukemia (ALL). However, studies on the prevalence of cytogenetic abnormalities and their correlation to clinical features in Chinese pediatric patients are limited, especially large-scale studies.

METHODS

We collected the cytogenetics and clinical data of 1541 children newly diagnosed with ALL between 2001 and 2014 in four Chinese hospitals, and retrospectively analyzed their clinical features, prognosis and risk factors associated with pediatric ALL.

RESULTS

All of these patients had karyotyping results, and some of them were tested for fusion genes by fluorescence in situ hybridization or reverse-transcription polymerase chain reaction. Overall, 930 cases (60.4%) had abnormal cytogenetics in this study, mainly including high hyperdiploidy (HHD, n=276, 17.9%), hypodiploidy (n=74, 4.8%), t(12;21)/TEL-AML1 (n=260, 16.9%), t(1;19)/E2A-PBX1 (n=72, 4.7%), t(9;22)/BCR-ABL (n=64, 4.2%), and t(v;11q23)/MLL rearrangements (n=40, 2.6%). The distribution of each cytogenetic abnormality was correlated with gender, age, white blood cell count at diagnosis, and immunophenotype. In addition, multivariate analysis suggested that t(v;11q23)/MLL rearrangements (OR: 2.317, 95%CI: 1.219-3.748, P=0.008) and t(9;22)/BCR-ABL (OR: 2.519, 95%CI: 1.59-3.992, P<0.001) were independent risk factors for a lower event-free survival (EFS) rate in children with ALL, while HHD (OR: 0.638, 95%CI: 0.455-0.894, P=0.009) and t(12;21)/TEL-AML1 (OR: 0.486, 95%CI: 0.333-0.707, P<0.001) were independent factors of a favorable EFS.

CONCLUSION

The cytogenetic characteristics presented in our study resembled other research groups, emphasizing the important role of cytogenetic and molecular genetic classification in ALL, especially in B-ALL.

Multicolor flow cytometry immunophenotyping and characterization of aneuploidy in pediatric B-cell precursor acute lymphoblastic leukemia

The aim of this study was to assess the incidence of DNA aneuploidy in Polish children with B-cell precursor acute lymphoblastic leukemia (BCP-ALL) and the relationship between aneuploidy and immunological phenotype, age, leukocyte count, S-phase fraction (SPF) and early response to induction chemotherapy assessed by the percentage of residual blast cells in bone marrow aspirates. The study group consisted of 267 patients. DNA content and immunophenotype were assessed in the bone marrow before treatment using multicolor flow cytometry (FC). DNA aneuploidy was detected in 50/267 (19%) patients. High hyperdiploidy was found to be associated with lower leukocyte count (p = 0.006) and common ALL immunophenotype. Flow cytometry analysis revealed that high hyperdiploid BCP-ALL patients showed significantly higher expression of CD9, CD20, CD22, CD58, CD66c, CD86 and CD123 antigens as compared to other groups of ploidy. In contrast, CD45 showed decreased expression. The percentage of leukemic blasts at diagnosis was lower in high hyperdiploid BCP-ALL cases than in diploid (79% vs. 85.7%, p = 0.001). The difference in minimal residual disease (MRD) levels on day 15 and 33 of induction therapy between analyzed groups was not significant.

This study showed that high hyperdiploidy is associated with lower WBC count and specific immunological phenotype. Flow cytometric evaluation of expression of selected antigens can be used for fast identification of markers of aneuploidy in pediatric BCP-ALL, before genetic tests results are available. Understanding the biological significance of aneuploidy in leukemia can potentially be exploited therapeutically using targeted therapies against specific blast cell subclones.

Blast size-specific flowcytometric ploidy assessment using FxCycleTM Violet dye and its correlation with conventional cytogenetic ploidy in pediatric precursor B-lineage acute lymphoblastic leukemia patients

INTRODUCTION

Numerical chromosomal abnormalities (aneuploidies), present in approximately 30%-50% of pediatric precursor B-lineage acute lymphoblastic leukemia (B-ALL) patients, are commonly identified through a laborious conventional cytogenetic (CG) technique. Flow cytometry (FCM) can identify both physical and fluorescent properties of cells together, and by using fluorescent nucleic-acid-binding dyes, FCM can identify variations in total nucleic-acid content of cells. FxCycle^TM Violet dye (FxCV) is a selective DNA-binding dye which permits simultaneous multiparametric immunophenotyping and cell-cycle/ploidy assessment in a single assay. To date, only two studies have demonstrated the feasibility of FxCV-aided FCM-ploidy analysis in B-ALL patients and only one of these studies have compared their results with CG-ploidy.

METHODOLOGY

Blast size-specific FCM-ploidy was prospectively analyzed using FxCV-dye in 109 pediatric B-ALL patients, and the results were compared with concurrent CG-ploidy status.

RESULTS

FCM-ploidy categorization was feasible in 98% of samples tested and the results were 82% concordant with CG-ploidy status. We observed significant correlation between DNA content and blast size (r = .823, P < .001) and could demonstrate size differences between diploid vs low-hyperdiploid (P = .025), diploid vs high-hyperdiploid (P < .001) and low- vs high-hyperdiploid blasts (P = .007).

CONCLUSION

FCM-ploidy assessment using FxCV dye is a reliable assay and the results closely concur with CG-based ploidy stratification and risk assessment. Using blast size-assisted DNA content analysis, the results of FCM-ploidy analysis can be further fine-tuned.

MLPA and DNA index improve the molecular diagnosis of childhood B-cell acute lymphoblastic leukemia

Aneuploidy occurs within a significant proportion of childhood B-cell acute lymphoblastic leukemia (B-ALL). Some copy number variations (CNV), associated with novel subtypes of childhood B-ALL, have prognostic significance. A total of 233 childhood B-ALL patients were enrolled into this study. Focal copy number alterations of ERG, IKZF1, PAX5, ETV6, RB1, BTG1, EBF1, CDKN2A/2B, and the Xp22.33/Yp11.31 region were assessed by Multiplex Ligation-dependent Probe Amplification (MLPA). The MLPA telomere kit was used to identify aneuploidy through detection of whole chromosome loss or gain. We carried out these procedures alongside measurement of DNA index in order to identify, aneuploidy status in our cohort. MLPA telomere data and DNA index correlated well with aneuploidy status at higher sensitivity than cytogenetic analysis. Three masked hypodiploid patients, undetected by cytogenetics, and their associated copy number neutral loss of heterozygosity (CN-LOH) were identified by STR and SNP arrays. Rearrangements of TCF3, located to 19p, were frequently associated with 19p deletions. Other genetic alterations including iAMP21, IKZF1 deletions, ERG deletions, PAX5^AMP, which have clinical significance or are associated with novel subtypes of ALL, were identified. In conclusion, appropriate application of MLPA aids the identifications of CNV and aneuploidy in childhood B-ALL.

MTHFR rs1801133 polymorphism is associated with increased risk of B-cell precursor lymphoblastic leukaemia with recurrent genetic aberrations of fetal origin

BACKGROUND

Childhood acute lymphoblastic leukaemia (ALL) is a heterogeneous disease associated with multiple risk factors including genetic susceptibility. Polymorphisms in folate genes have been associated with a protective effect against ALL, although some studies contradict these findings. We aimed to test whether there is an association between the MTHFR rs1801133 variant and the occurrence of B-cell precursor ALL (BCP-ALL) taking in account molecularly distinct subtypes of fetal origin.

METHODS

We performed a case-control genotyping study with 2067 samples, 1309 ALL and 758 controls, from children aged ≤ 15 years for MTHFR rs1801133 polymorphism. Risk associations were calculated by odds ratios estimated with unconditional logistic regression, adjusted for frequency-matched ethnic groups.

RESULTS

Overall, MTHFR rs1801133 does not impact ALL risk in children with more than 6 years of age. A significant positive association for MTHFR rs1801133 variant was found for ALL with KMT2A-r in the dominant model (adj. OR, 1.48, 95 % CI, 1.01-2.17), while ETV6-RUNX1 and Hyperdiploid subgroups have shown a borderline effect (adj. OR, 1.33, 95 % CI, 0.99-1.78).

CONCLUSIONS

The polymorphism MTHFR rs1801133 increased the risk of infant ALL in Brazilian population.

Nationwide survey of pediatric hypodiploid acute lymphoblastic leukemia in Japan

BACKGROUND

Ploidy is a highly significant prognostic factor for pediatric acute lymphoblastic leukemia (ALL). Children with hypodiploid ALL have poor outcomes despite current intensive chemotherapy. Little has been investigated with regard to hypodiploid ALL in Japanese children.

METHODS

We retrospectively collected clinical data on hypodiploid ALL cases from the registries of prospective multicenter trials conducted by the four independent clinical study groups in Japan between 1997 and 2012.

RESULTS

A total of 117 ALL patients with hypodiploidy were analyzed in this study. There were 101, eight, and eight patients with 45, 44, and fewer than 44 chromosomes, respectively. The 5 year overall survival rates differed significantly: 86.0%, 87.5%, and 62.5% for patients with 45, 44, and fewer than 44 chromosomes, respectively (P = 0.037). Of the eight patients with 44 chromosomes, seven were alive, including five patients who maintained complete remission without undergoing hematopoietic stem cell transplantation (HSCT). Of the eight patients with fewer than 44 chromosomes, six were good responders to prednisolone and none had induction failure, but the relapse rate was high (5/8). No patients had central nervous system relapse. Four patients underwent HSCT after relapse, but only one survived.

CONCLUSIONS

Outcomes of Japanese ALL patients with fewer than 44 chromosomes were poor, as previously reported in other countries. Although the sample size was small, patients with 44 chromosomes had better prognoses than those previously reported. Further studies including international collaboration are needed to improve outcomes for pediatric ALL patients with fewer than 44 chromosomes.

FxCycle™ Based Ploidy Correlates with Cytogenetic Ploidy in B-Cell Acute Lymphoblastic Leukemia and Is Able to Detect the Aneuploid Minimal Residual Disease Clone

BACKGROUND

Flow cytometry (FCM) is a simple, sensitive, and specific technique that can potentially determine DNA ploidy in B-cell precursor ALL (BCP-ALL) and is complementary to cytogenetics.

METHODS

A prospective FCM DNA ploidy analysis using FxCycle™ Violet (assay sensitivity 0.01%) was done in 125 consecutive new cases of BCP-ALL (90 cases <15 years of age) and compared with corresponding cytogenetic ploidy (karyotyping and/or FISH) data wherever available. This assay was also subsequently evaluated for detection of residual aneuploid clone in few BCP-ALL cases.

RESULTS

Of the total 125 BCP-ALL cases evaluated, flow ploidy analysis revealed diploidy (DI 0.96-1.05) in 44.8% (n = 56), low-hyperdiploidy (DI 1.06 to 1.15) in 13.6% (n = 17), high-hyperdiploidy (DI 1.16-1.39) in 32.8% (n = 41) and near-tetraploidy (DI ≥ 1.80) in 2.4% (n = 3) cases. The high risk sub-group of low-hypodiploidy (DI 0.70 to 0.88)/near-triploidy (DI 1.40 to 1.79) constituted 5.6% (n = 7) cases while there was only one case with haploidy (DI 0.58). Overall, high concordance of 90.4% (n = 113) was noted between the combined cytogenetics ploidy and FCM ploidy. Of the total discordant cases (n = 12), the maximum discordance was seen in the low-hyperdiploid DI subgroup (n = 10), which included seven cases with low DNA index high hyperdiploidy (LDI-HHD). FCM DNA ploidy assay was able to detect the residual clone in all six MRD positive aneuploid cases evaluated.

CONCLUSIONS

FxCycle™ based DNA ploidy ascertains strong correlation with cytogenetic profiles and yields complementary information that can be used by the cytogenetics laboratories or otherwise. © 2019 International Clinical Cytometry Society.

Impact of cytogenetic abnormalities in adults with Ph-negative B-cell precursor acute lymphoblastic leukemia

Multiple cytogenetic subgroups have been described in adult Philadelphia chromosome (Ph)-negative B-cell precursor (BCP) acute lymphoblastic leukemia (ALL), often comprising small numbers of patients. In this study, we aimed to reassess the prognostic value of cytogenetic abnormalities in a large series of 617 adult patients with Ph-negative BCP-ALL (median age, 38 years), treated in the intensified Group for Research on Adult Acute Lymphoblastic Leukemia (GRAALL)-2003/2005 trials. Combined data from karyotype, DNA index, fluorescence in situ hybridization, and polymerase chain reaction screening for relevant abnormalities were centrally reviewed and were informative in 542 cases (88%), allowing classification in 10 exclusive primary cytogenetic subgroups and in secondary subgroups, including complex and monosomal karyotypes. Prognostic analyses focused on cumulative incidence of failure (including primary refractoriness and relapse), event-free survival, and overall survival. Only 2 subgroups, namely t(4;11)/KMT2A-AFF1 and 14q32/IGH translocations, displayed a significantly worse outcome in this context, still observed after adjustment for age and after censoring patients who received allogeneic stem cell transplantation (SCT) in first remission at SCT time. A worse outcome was also observed in patients with low hypodiploidy/near triploidy, but this was likely related to their higher age and worse tolerance to therapy. The other cytogenetic abnormalities, including complex and monosomal karyotypes, had no prognostic value in these intensive protocols designed for adult patients up to the age of 60 years.

Children with low-risk acute lymphoblastic leukemia are at highest risk of second cancers

BACKGROUND

The improved survival rates for childhood acute lymphoblastic leukemia (ALL) may be jeopardized by the development of a second cancer, which has been associated with thiopurine therapy.

PROCEDURE

We retrospectively analyzed three sequential Nordic Society of Paediatric Haematology and Oncology's protocols characterized by increasing intensity of thiopurine-based maintenance therapy. We explored the risk of second cancer in relation to protocols, risk group, thiopurine methyltransferase (TPMT) activity, ALL high hyperdiploidy (HeH), and t(12;21)[ETV6/RUNX1].

RESULTS

After median 9.5 years (interquartile range, 5.4-15.3 yrs) of follow-up, 40 of 3,591 patients had developed a second cancer, of whom 38 had non-high-risk B-cell precursor ALL. Patients with standard-risk ALL, who received the longest maintenance therapy, had the highest adjusted hazard of second cancer (hazard ratio [HR], intermediate vs. standard risk: 0.16, 95% CI: 0.06-0.43, P < 0.001; HR, high vs. standard risk: 0.09, 95% CI: 0.02-0.49, P = 0.006); no significant effects of protocol, age, or white blood cell count at diagnosis, ALL HeH, or t(12;21)[ETV6/RUNX1] were observed. A subset analysis on the patients with standard-risk ALL did not show an increased hazard of second cancer from either HeH or t(12;21) (adjusted HR 2.02, 95% CI: 0.69-5.96, P = 0.20). The effect of low TPMT low activity was explored in patients reaching maintenance therapy in clinical remission (n = 3,368); no association with second cancer was observed (adjusted HR 1.43, 95% CI: 0.54-3.76, P = 0.47).

CONCLUSIONS

The rate of second cancer was generally highest in patients with low-risk ALL, but we could not identify a subset at higher risk than others.

Aneuploidy identification in pre-B acute lymphoblastic leukemia patients at diagnosis by Multiplex Ligation-dependent Probe Amplification (MLPA)

Three-quarters of the patients with acute lymphoblastic leukemia (ALL), show numerical or structural chromosomal alterations, which are important factors in leukemogenesis. The use of Multiplex Ligation-dependent Probes Amplification (MLPA) has been mainly limited for searching copy number alterations of genes, suggesting that MLPA could detect numerical alterations in cancer. However, the use of MLPA in pediatrics to analyze subtelomeric sequences for aneuploidy detection has not been considered in previous studies. The aim of this study was to identify aneuploidy for the first time using MLPA and correlate the results with karyotype and DNA-index (DI), from preB ALL patients. Forty-two bone marrow samples were analyzed by cytogenetics and flow cytometry to determine the DI. The chromosomal gains and/or losses were detected by the SALSA MLPA P036 Subtelomere Mix 1 probemix^®. The chromosomal number matched in 36 out of 42 samples between MLPA and karyotype (R²=0.7829, p=3.7×10^-10), 18/42 between MLPA and DI (R²=0.1556, p=0.023), and 20/42 between karyotype and DI (R²=0.1509, p=0.015). MLPA results correlated with karyotype and DI. The use of MLPA led us to identify a gained marker chromosome. Our results indicate that MLPA could be a useful and fast alternative tool for aneuploidy identification in pediatric leukemia.

Near-haploid and low-hypodiploid acute lymphoblastic leukemia: two distinct subtypes with consistently poor prognosis

Hypodiploidy <40 chromosomes is an uncommon genetic feature of acute lymphoblastic leukemia (ALL) in both children and adults. It has long been clear by cytogenetic analyses, and recently confirmed by mutational profiling, that these cases may be further subdivided into 2 subtypes: near-haploid ALL with 24 to 30 chromosomes and low-hypodiploid ALL with 31 to 39 chromosomes. Both groups are associated with a very poor prognosis, and these patients are among those who could benefit most from novel treatments.

Advances and issues in flow cytometric detection of immunophenotypic changes and genomic rearrangements in acute pediatric leukemia

Flow cytometry with its rapidly increasing applications has been using to aid the diagnosis of hematological disorders for more than two decades. It is also the most commonly used technology in childhood leukaemia diagnosis, characterization, prognosis prediction and even in the decision making of targeted therapy. Leukemia cells can be recognized by virtue of unique cell marker combinations, visualized with monoclonal antibodies conjugated and detected by flow cytometry. Currently, such instruments allow the detection of eight or more markers by providing a comprehensive description of the leukemic cell phenotype to facilitate their identification, especially in detecting and monitoring of minimal residual disease (MRD) during treatment. Additionally, the flow cytometric DNA index (DI) can identify biclonality at diagnosis and distinguish persistent aneuploid leukemia during induction therapy, when the standard cytogenetic and morphologic techniques fail to do so. This review focuses on the latest advances and application issues about some of flow cytometric diagnostic and prognostic applications for acute pediatric leukemia.

Hyperdiploidy with 58-66 chromosomes in childhood B-acute lymphoblastic leukemia is highly curable: 58951 CLG-EORTC results

The aim of our study was to analyze the factors contributing to heterogeneity of prognosis in patients with hyperdiploidy>50 chromosomes (HD>50), a group of B-cell precursor acute lymphoblastic leukemia with favorable outcome. The 541 HD>50 patients registered prospectively in the 58951 European Organisation for Research and Treatment of Cancer (EORTC) Children's Leukemia Group (CLG) trial, identified by karyotype (446 patients) and by DNA index (DI) (490 patients), had a 6-year event-free survival (EFS) of 89.0% (standard error [SE] = 1.5%) and a 6-year overall survival (OS) of 95.9% (SE = 0.9%). The strongest prognostic factor was the modal number of chromosomes (MNC): the 6-year EFS of 51-53, 54-57, and 58-66 MNC groups were 80%, 89%, and 99%, respectively (P < .0001). Ploidy assessed by DI was also a favorable factor: the higher the DI, the better the outcome. The 6-year EFS of the 3 subgroups of DI < 1.16/≥1.16-<1.24/≥1.24 were 83%, 90%, and 95%, respectively (P = .009). All usual combinations of trisomies (chromosomes 4, 10, 17, 18) were significant favorable factors but had lower EFS when MNC was lower than 58. In multivariate analysis, MNC remained the strongest factor. Consequently, the best indicator for excellent outcome was ploidy assessed by karyotype because patients with 58-66 chromosomes stood every chance of being cured (OS of 100% at 6-year follow-up) with less-intensive therapy. This trial was registered at www.clinicaltrials.gov as #NCT00003728. Registered: http://www.eortc.org/, http://clinicaltrials.gov/show/NCT00003728.