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5-year overall survival rates have surpassed 90% for childhood acute lymphocytic leukaemia, but survivors are at risk for permanent health sequelae. Although event-free survival appropriately represents the outcome for cancers with poor overall survival, this metric is inadequate when cure rates are high but challenged by serious, persistent complications. Accordingly, a group of experts in paediatric haematology–oncology, representative of 17 international acute lymphocytic leukaemia study groups, launched an initiative to construct a measure, designated severe toxicity-free survival (STFS), to quantify the occurrence of physician-prioritised toxicities to be integrated with standard cancer outcome reporting. Five generic inclusion criteria (not present before cancer diagnosis, symptomatic, objectifiable, of unacceptable severity, permanent, or requiring unacceptable treatments) were used to assess 855 health conditions, which resulted in inclusion of 21 severe toxicities. Consensus definitions were reached through a modified Delphi process supplemented by two additional plenary meetings. The 21 severe toxicities include severe adverse health conditions that substantially affect activities of daily living and are refractory to therapy (eg, refractory seizures), are without therapeutic options (eg, blindness), or require substantially invasive treatment (eg, cardiac transplantation). Incorporation of STFS assessment into clinical trials has the potential to improve and diversify treatment strategies, focusing not only on traditional outcome events and overall survival but also the frequencies of the most severe toxicities. The two major aims of this Review were to: prioritise and define unacceptable long-term toxicity for patients with childhood acute lymphocytic leukaemia, and define how these toxicities should be combined into a composite quantity to be integrated with other reported outcomes. Although STFS quantifies the clinically unacceptable health tradeoff for cure using childhood acute lymphocytic leukaemia as a model disease, the prioritised severe toxicities are based on generic considerations of relevance to any other cancer diagnosis and age group.

Genetic analysis of leukemic clones in monozygotic twins with concordant acute lymphoblastic leukemia (ALL) has proved a unique opportunity to gain insight into the molecular phylogenetics of leukemogenesis. Using whole-genome sequencing, we characterized constitutional and somatic single nucleotide variants/insertion-deletions (indels) and structural variants in a monozygotic twin pair with concordant ETV6-RUNX1+B-cell precursor ALL (BCP-ALL). In addition, digital PCR (dPCR) was applied to evaluate the presence of and quantify selected somatic variants at birth, diagnosis, and remission. A shared somatic complex rearrangement involving chromosomes 11, 12, and 21 with identical fusion sequences in leukemias of both twins offered direct proof of a common clonal origin. The ETV6-RUNX1fusion detected at diagnosis was found to originate from this complex rearrangement. A shared somatic frameshift deletion in UBA2was also identified in diagnostic samples. In addition, each leukemia independently acquired analogous deletions of 3 genes recurrently targeted in BCP-ALLs (ETV6, ATF7IP, and RAG1/RAG2), providing evidence of a convergent clonal evolution only explained by a strong concurrent selective pressure. Quantification of the UBA2deletion by dPCR surprisingly indicated it persisted in remission. This, for the first time to our knowledge, provided evidence of a UBA2variant preceding the well-established initiating event ETV6-RUNX1. Further, we suggest the UBA2deletion exerted a leukemia predisposing effect and that its essential role in Small Ubiquitin-like Modifier (SUMO) attachment (SUMOylation), regulating nearly all physiological and pathological cellular processes such as DNA-repair by nonhomologous end joining, may hold a mechanistic explanation for the predisposition.

Genetic analysis of leukemic clones in monozygotic twins with concordant acute lymphoblastic leukemia (ALL) has proved a unique opportunity to gain insight into the molecular phylogenetics of leukemogenesis. Using whole-genome sequencing, we characterized constitutional and somatic single nucleotide variants/insertion-deletions (indels) and structural variants in a monozygotic twin pair with concordant ETV6-RUNX1+ B-cell precursor ALL (BCP-ALL). In addition, digital PCR (dPCR) was applied to evaluate the presence of and quantify selected somatic variants at birth, diagnosis, and remission. A shared somatic complex rearrangement involving chromosomes 11, 12, and 21 with identical fusion sequences in leukemias of both twins offered direct proof of a common clonal origin. The ETV6-RUNX1 fusion detected at diagnosis was found to originate from this complex rearrangement. A shared somatic frameshift deletion in UBA2 was also identified in diagnostic samples. In addition, each leukemia independently acquired analogous deletions of 3 genes recurrently targeted in BCP-ALLs (ETV6, ATF7IP, and RAG1/RAG2), providing evidence of a convergent clonal evolution only explained by a strong concurrent selective pressure. Quantification of the UBA2 deletion by dPCR surprisingly indicated it persisted in remission. This, for the first time to our knowledge, provided evidence of a UBA2 variant preceding the well-established initiating event ETV6-RUNX1. Further, we suggest the UBA2 deletion exerted a leukemia predisposing effect and that its essential role in Small Ubiquitin-like Modifier (SUMO) attachment (SUMOylation), regulating nearly all physiological and pathological cellular processes such as DNA-repair by nonhomologous end joining, may hold a mechanistic explanation for the predisposition.

Asparaginase treatment is a mainstay in contemporary treatment of acute lymphoblastic leukemia (ALL), but substantial asparaginase-related toxicity may lead to jeopardized protocol compliance and compromises survival. We investigated the association between risk of asparaginase-associated toxicities (AspTox) and asparaginase enzyme activity (AEA) levels in 1155 children aged 1.0 to 17.9 years, diagnosed with ALL between July 2008 and March 2016, and treated according to the Nordic Society of Pediatric Hematology and Oncology (NOPHO) ALL2008 protocol. Patients with ≥2 blood samples for AEA measurement drawn 14 ± 2 days after asparaginase administration were included (6944 trough values). AEA was measurable (or >0 IU/L) in 955 patients, whereas 200 patients (17.3%) had asparaginase inactivation and few AspTox recorded. A time-dependent multiple Cox model of time to any first asparaginase-associated toxicity adjusted for sex and age was used. For patients with measurable AEA, we found a hazard ratio (HR) of 1.17 per 100 IU/L increase in median AEA (95% confidence interval [CI], 0.98-1.41; P = .09). For pancreatitis, thromboembolism, and osteonecrosis, the HRs were 1.40 (95% CI, 1.12-1.75; P = .002), 0.99 (95% CI, 0.70-1.40; P = .96), and 1.36 (95% CI, 1.04-1.77; P = .02) per 100 IU/L increase in median AEA, respectively. No significant decrease in the risk of leukemic relapse was found: HR 0.88 per 100 IU/L increase in AEA (95% CI, 0.66-1.16; P = .35). In conclusion, these results emphasize that overall AspTox and relapse are not associated with AEA levels, yet the risk of pancreatitis and osteonecrosis increases with increasing AEA levels.

Supplemental Digital Content is available in the text

Childhood, adolescent, and young adult cancer survivors are at increased risk of reduced bone mineral density. Clinical practice surveillance guidelines are important for timely diagnosis and treatment of these survivors, which could improve bone mineral density parameters and prevent fragility fractures. Discordances across current late effects guidelines necessitated international harmonisation of recommendations for bone mineral density surveillance. The International Late Effects of Childhood Cancer Guideline Harmonization Group therefore established a panel of 36 experts from ten countries, representing a range of relevant medical specialties. The evidence of risk factors for very low and low bone mineral density and fractures, surveillance modality, timing of bone mineral density surveillance, and treatment of very low and low bone mineral density were evaluated and critically appraised, and harmonised recommendations for childhood, adolescent, and young adult cancer survivors were formulated. We graded the recommendations based on the quality of evidence and balance between potential benefits and harms. Bone mineral density surveillance is recommended for survivors treated with cranial or craniospinal radiotherapy and is reasonable for survivors treated with total body irradiation. Due to insufficient evidence, no recommendation can be formulated for or against bone mineral density surveillance for survivors treated with corticosteroids. This surveillance decision should be made by the survivor and health-care provider together, after careful consideration of the potential harms and benefits and additional risk factors. We recommend to carry out bone mineral density surveillance using dual-energy x-ray absorptiometry at entry into long-term follow-up, and if normal (Z-score > −1), repeat when the survivor is aged 25 years. Between these measurements and thereafter, surveillance should be done as clinically indicated. These recommendations facilitate evidence-based care for childhood, adolescent, and young adult cancer survivors internationally.

Central nervous system (CNS) involvement by cytospin is associated with increased risk of relapse in childhood acute lymphoblastic leukemia. We investigated if flow cytometric analysis of cerebrospinal fluid (CSF) at diagnosis improves the prediction of relapse. This prospective cohort study included patients (1.0–17.9 years) treated according to the Nordic Society of Pediatric Hematology and Oncology ALL2008 protocol. CSF flow cytometry samples were obtained at 17 centers, preserved with Transfix®, and analyzed at a central laboratory. One-hundred and seventy-one (25.4%) of 673 patients were positive by flow cytometry (CNSflow+). The 4-year cumulative incidence of relapse was higher for patients with cytospin positivity (CNScyto+) (17.1% vs. 7.5%), CNSflow+(16.5% vs. 5.6%), and cytospin and/or flow positivity (CNScomb+) (16.7% vs. 5.1%). In Cox regression analysis stratified by immunophenotype and minimal residual disease day 29 and adjusted by sex, predictors of relapse were age (hazard ratio [HR] 1.1, 95% CI 1.1–1.2, P?

Pathogenic germline variants in ETV6 have been associated with familial predisposition to thrombocytopenia and hematological malignancies, predominantly childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). In addition, overrepresentation of a high hyperdiploid subtype and older age at diagnosis have been reported among sporadic BCP-ALL cases with germline variants in ETV6. We studied a family with 2 second-degree relatives who developed childhood high hyperdiploid BCP-ALL at ages 8 and 12 years, respectively. A constitutional balanced reciprocal translocation t(12;14)(p13.2;q23.1) was discovered in both patients by routine karyotyping at diagnosis and, subsequently, in 7 healthy family members who had not experienced hematological malignancies. No carriers had thrombocytopenia. Whole-genome sequencing confirmed the translocation, resulting in 2 actively transcribed but nonfunctional fusion genes, causing heterozygous loss and consequently monoallelic expression of ETV6. Whole-genome sequencing analysis of the affected female subjects’ leukemia excluded additional somatic aberrations in ETV6 and RTN1 as well as shared somatic variants in other genes. Expression studies, performed to confirm decreased expression of ETV6, were not conclusive. We suggest that germline aberrations resulting in monoallelic expression of ETV6 contribute to leukemia susceptibility, whereas more severe functional deficiency of ETV6 is required for developing THC5. To our knowledge, this report is the first of a constitutional translocation disrupting ETV6 causing predisposition to childhood ALL.

The antileukaemic drug 6-mercaptopurine is converted into thioguanine nucleotides (TGN) and incorporated into DNA (DNA-TG), the active end metabolite. In a series of genome-wide association studies, we analysed time-weighted means (wm) of erythrocyte concentrations of TGN (Ery-TGN) and DNA-TG in 1009 patients undergoing maintenance therapy for acute lymphoblastic leukaemia (ALL). In discovery analyses (454 patients), the propensity for DNA-TG incorporation (wmDNA-TG/wmEry-TGN ratio) was significantly associated with three intronic SNPs in NT5C2(top hit: rs72846714; P= 2.09 × 10−10, minor allele frequency 15%). In validation analyses (555 patients), this association remained significant during both early and late maintenance therapy (P= 8.4 × 10−6and 1.3 × 10−3, respectively). The association was mostly driven by differences in wmEry-TGN, but in regression analyses adjusted for wmEry-TGN (P< 0.0001), rs72846714-A genotype was also associated with a higher wmDNA-TG (P= 0.029). Targeted sequencing of NT5C2did not identify any missense variants associated with rs72846714 or wmEry-TGN/wmDNA-TG. rs72846714 was not associated with relapse risk, but in a separate cohort of 180 children with relapsed ALL, rs72846714-A genotype was associated with increased occurrence of relapse-specific NT5C2gain-of-function mutations that reduce cytosol TGN levels (P= 0.03). These observations highlight the impact of both germline and acquired mutations in drug metabolism and disease trajectory.

Supplemental Digital Content is available in the text.Posterior reversible encephalopathy syndrome (PRES) in children with acute lymphoblastic leukemia has been increasingly recognized as a clinicoradiological entity. Our aim was to describe the incidence of PRES in pediatric patients with ALL, identify its risk factors, and examine its prognostic importance. For this research, we conducted a systematic, retrospective review of the patient records in a population-based series of children with acute lymphoblastic leukemia (n=643) treated in Finland from 1992 to 2008. Of the patients with ALL, 4.5% (n=29) developed radiologically confirmed PRES, of which 28 cases occurred during induction. Hypertension (P=0.006; odds ratio [OR], 4.10, confidence interval [CI], 1.50-11.25), constipation (P=0.001; OR, 5.60; CI, 2.02-15.52), and >14 days of alkalinization (P=0.017; OR, 3.27; CI, 1.23-8.68) were significant independent risk factors for PRES. One-third of the patients developed epilepsy. Relapses occurred significantly more often in those patients with PRES (P=0.001), which was associated with worse overall survival (P=0.040; 5-year survival=75.9% [60.3%-91.4%] vs. 88.4% [85.8%-90.9%]). Using NOPHO-ALL 92/2000 protocols, PRES is a significant early complication of therapy in ALL, and was associated with a poorer prognosis and significant neurological morbidity.

Hepatotoxicity is a known toxicity to treatment of childhood acute lymphoblastic leukemia. Hepatotoxicity occurs during maintenance therapy and is caused by metabolites of 6-Mercaptopurine (6 MP) and Methotrexate (MTX). Our objective was to investigate the association between alanine aminotransferases (ALAT) levels and relapse rate. We included 385 patients enrolled in the NOPHO ALL-92 protocol. Data on ALAT levels, 6 MP and MTX doses, cytotoxic MTX/6 MP metabolites, and thiopurine methyltransferase (TPMT) activity were prospectively registered. In total, 91% of the patients had a mean ALAT (mALAT) level above upper normal limit (40 IU/L) and ALAT levels were positively correlated to 6 MP doses (rs=0.31; P<0.001). In total, 47 patients suffered a relapse, no difference in mALAT levels were found in these compared with nonrelapse patients (median, 107 vs. 98 IU/L; P=0.39). mALAT levels in patients classified as TPMThigh activity (TPMTWT) were higher than in TPMTlow-activity patients (median, 103 vs. 82 IU/L; P=0.03). In a Cox regression model risk of relapse was not associated with ALAT levels (P=0.56). ALAT levels increased 2.7%/month during the last year of maintenance therapy (P<0.001). In conclusion, elevated ALAT levels are associated with TPMTWTand may indicate treatment adherence in these patients. If liver function is normal, elevated ALAT levels should not indicate treatment adaptation.

Supplemental Digital Content is available in the text.We investigated efficacy and toxicity of replacing conventional triple (cytarabine, methotrexate, and hydrocortisone) intrathecal therapy (TIT) with liposomal cytarabine during maintenance therapy among 40 acute lymphoblastic leukemia patients. Twenty-eight of 29 patients in the TIT arm received TIT and 9/11 in the liposomal cytarabine arm received liposomal cytarabine. Arachnoiditis occurred in all initial 5 patients given liposomal cytarabine and intrathecal prednisolone succinate. Subsequently liposomal cytarabine was given with systemic dexamethasone. Neurotoxicity occurred at 6/27 liposomal cytarabine administrations with concomitant dexamethasone (22%). More liposomal cytarabine-treated patients experienced neurotoxicity in relation to intrathecal therapy during at least 1 cycle compared with TIT-treated patients (6/9 [67%] vs. 3/28 [11%], P=0.002). Apart from intermittent lower extremity sensory pain in 1 liposomal cytarabine-treated patient, no permanent adverse neurological sequelae were observed. In intention-to-treat analysis, projected 5-year event-free survival (pEFS-5y) was borderline higher for patients in the liposomal cytarabine arm compared with the TIT arm (1.0 vs. 0.69, P=0.046). However, pEFS-5y and projected 5-year relapse-free survival did not differ signficantly between patients treated with liposomal cytarabine or TIT (1.0 vs. 0.73, P=0.10; 1.0 vs. 0.76, P=0.12). Larger prospective trials are needed to explore whether liposomal cytarabine should be used as first-line prevention of relapse.

Childhood cancer survivors are thought to be at risk of psychological difficulties. We examined the prevalence of depressive symptoms and mental well-being in adult long-term survivors of childhood acute lymphoblastic leukemia (ALL) at a mean age of 20 years after the cessation of therapy. Depressive symptoms were assessed with Beck Depression Inventory (BDI-21) and mental distress with General Health Questionnaire (GHQ-12) among 73 ALL survivors and 146 healthy controls. The ALL survivors obtained significantly lower BDI scores (P=0.046) compared with the controls, indicating less depressive symptoms among the ALL survivors. BDI scores indicated a significantly less frequent moderate or severe depression in the ALL survivors compared with the controls (P=0.039). BDI scores indicated no depression in 80.8 of the ALL survivors and 73.3 of the control group. The female ALL survivors obtained lower BDI scores than did the female controls (P=0.005). No difference was found in GHQ-12 scores between the survivors and the controls. Survivors of ALL reported fewer depressive symptoms and equal mental well-being compared with healthy controls. Our findings support the idea that childhood leukemia survivors' subjective experience of well-being is possibly affected by repressive adaptive style.

The purpose of this study was to find out the incidence of and clinical risk factors for magnetic resonance imaging (MRI)-detected osteonecrosis (ON) in children treated for lymphoma or solid tumors.

Treatment of childhood leukemia may cause perfusion defects in the brain observed by SPECT. Perfusion MRI is a novel method to study brain perfusion which has not been used previously in this setting. This study was performed to compare SPECT with perfusion MRI in patients with acute lymphoblastic leukemia (ALL) after treatment. Nineteen children or young adults underwent perfusion MRI at the cessation of treatment (n = 9) or 4–8 years after the treatment (n = 10). Seventeen of them also underwent SPECT at the time of MRI (within 0–3 days, n = 14) or a couple of months later (1.5–6 months, n = 3). SPECT images and relative cerebral blood volume (CBV) and cerebral blood flow (CBF) maps from perfusion MRI were analyzed visually. Relative CBV ratios of gray matter to white matter and thalamus to white matter were also calculated from the perfusion MRI. Perfusion MRI did not show any focal perfusion defects, while small defects were observed by SPECT in five of 17 children (29%) in the basal, frontal or temporal areas on the left. No significant differences were observed by perfusion MRI in the relative CBV ratios in the different treatment groups. Time since treatment, age at diagnosis, brain irradiation, or findings in conventional MRI or SPECT did not have any effect on the relative perfusion values either. SPECT may show small perfusion defects after treatment for childhood leukemia which are not visible by perfusion MRI. The clinical significance or prognosis of these defects is not known. Med Pediatr Oncol 2003;40:88–92. © 2003 Wiley-Liss, Inc.

The objective was to evaluate whether motor nervous pathways are affected when patients are treated for childhood acute lymphoblastic leukemia (ALL). Thirty-two children with ALL were studied at the end of treatment by means of motor evoked potentials (MEPs) elicited by magnetic stimulation (MS) transcranially and peripherally and underwent a detailed neurological examination. Thirty-two healthy children matched with them for age, sex, and height served as a control group. The latencies of the MEPs were significantly prolonged along the entire motor nervous pathway in the patients with ALL compared with the healthy controls, indicating demyelination in the thick motor fibres. The MEP amplitudes of the distal extremities elicited by stimulation at the brachial plexus and LV spinal level were significantly lowered in the patients treated for ALL, also indicating anatomical or functional loss of descending motor fibres and/or muscle fibres. The MEP amplitudes elicited by cortical MS showed wider variation and no clear abnormalities were found. Neurological signs and symptoms were common after treatment: 41% of the patients had depressed deep tendon reflexes, 31% had fine motor difficulties and 63% gross motor difficulties, and 34% had dysdiadochokinesia. The conduction delay within the peripheral nerve was related to the post-therapeutic interval after administration of vincristine and the lesions within the CNS to the number of injections of intrathecal methotrexate. The present results show adverse effects of the ALL treatment on the entire motor nervous pathways. In our experience, the measurement of MEPs by MS provides an objective, painless, and practical tool for assessing the treatment-related neurotoxicity in both the CNS and the peripheral nerves. These disturbances in the motor nervous pathways at the end of treatment raise the question of the long-term effects of ALL treatment on the motor nerve tracts, and have led us to employ MEPs to study these effects in long-term survivors of ALL. Med. Pediatr. Oncol. 36:345–351, 2001. © 2001 Wiley-Liss, Inc.

Treatment of childhood acute lymphoblastic leukemia (ALL) may cause structural and functional brain damage. To find out the incidence of white matter changes during therapy, a prospective MRI study was designed, and the findings were correlated with neuropsychological evaluation. Thirty-three children with ALL underwent serial cranial MRI before, during, and after therapy. Twenty-eight of these children underwent also neuropsychological assessment at the end of treatment. They all received intravenous and intrathecal methotrexate for central nervous system (CNS) therapy, 15 patients received cranial irradiation in addition. Transient high-intensity white matter changes were observed by MRI in three children 9% (95% CI, 2–24%) who received chemotherapy only. The high-intensity changes were most prominent in the frontal lobes in two of these children. The children with white matter changes were significantly younger than those with normal MRI (2.8 vs. 7.4 years; mean). There was no correlation between neuropsychological tests and white matter changes, except in attention and in tests referring to the frontal areas in general. White matter changes are occasionally observed during therapy with the current Nordic protocols. Young children may be more susceptible to developing white matter changes after repeated intravenous methotrexate injections. There is no systematic correlation between neuropsychological deficits and MRI findings. Med. Pediatr. Oncol. 35:456–461, 2000. © 2000 Wiley-Liss, Inc.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Premature discontinuation of asparaginase reduces cure rate in contemporary acute lymphoblastic leukemia (ALL) treatment. One of the commonest causes of asparaginase truncation is asparaginase-associated pancreatitis (AAP). We prospectively registered AAP during treatment of 2,448 consecutive Nordic/Baltic ALL patients aged 1.0-45.9 years treated according to the Nordic Society of Pediatric Hematology and Oncology (NOPHO) ALL2008 protocol (7/2008-10/2018).

No relevant conflicts of interest to declare.

No relevant conflicts of interest to declare.

Introduction:Asparaginase is a cornerstone in treatment of childhood acute lymphoblastic leukemia (ALL). However, balancing positive anti-leukemic effect against toxicities has proven difficult. A frequent toxicity is allergy; 13% of children treated according to the Nordic NOPHO ALL2008 protocol develop an allergic reaction to pegylated asparaginase (PEG-asparaginase) causing acute morbidity and necessitating truncation of therapy. (Henriksen et al, PBC, 2014 and 2017).

No relevant conflicts of interest to declare.

Although aberrant DNA methylation has been observed previously in acute lymphoblastic leukemia (ALL), the patterns of differential methylation have not been comprehensively determined in all subtypes of ALL on a genome-wide scale. The relationship between DNA methylation, cytogenetic background, drug resistance and relapse in ALL is poorly understood.

Development of cytogenetic methods has contributed to the understanding that ALL is not a homogenous disease. Detection of structural and numerical alterations in the chromosomes of lymphoblasts has identified several different ALL subgroups. G-banding reveals about 60–70% of these changes. The development of FISH and PCR methods has decreased the proportion of apparently normal karyotype to less than 20%. Still a part of ALL patients have no chromosomal aberrations detected with conventional cytogenetics. It seems likely, however, that ALL with a normal karyotype reflects rather our inadequate capability to detect all possible aberrations than a true normality of the lymphoblast genome. Microarray methods offer an effective tool to define novel cytogenetic changes in ALL. In our study characterizing and evaluating ALL in adolescents and young adults aged 10–25 years in Finland, we analyzed patients diagnosed during 1990–2007 (n=231). Eighty-nine patients had normal (n=80) or failed (n=9) karyotype at diagnosis. DNA from initial samples was available for 27 of these 89 patients. 26 patients had normal karyotypes, for one patient the karyotype analysis failed by G-banding at diagnosis. The key clinical characteristics of the 27 patients did not differ from the rest of the patients with normal or failed karyotype. Genomic DNA was extracted from diagnostic bone marrow samples. Digestion, labeling and hybridization of DNA was performed according to the Agilent protocol version 2.0 for 44K arrays. Labeled samples were hybridized against gender matched reference DNAs to Human Genome CGH 44B oligo microarray slides (Agilent Technologies Santa Clara, CA, USA). For data-analysis Agilent’s CGH Analytics software version 3.5 was used. The starting and ending points of the aberrations were confirmed by the ADM-2 algorithm with 10.0 threshold. The immunophenotype of the patients was as follows: T-cell ALL 8/27 patients, precursor B ALL 13/27, mixed lineage 5/27 (according to the European Group for the Immunological Characterization of Leukemias), not known 1/27. Seventeen patients had normal karyotype and no other marker for MRD follow-up, while 9 patients had either immunoglobulin and/or T-cell receptor gene rearrangement (n=8) or over-expression of Willms Tumor gene 1 (WT1) (n=1). In total 58 aberrations were detected in the 27 patient samples (1–7 aberrations per sample, mean 2.1) (Figure 1). Four samples (15%) did not show any aberration (two with immunoglobulin and/or T-cell receptor gene rearrangements). Losses were detected in 20/27 cases and gains in 10/27 cases. Cases with losses only were more frequent (n=13, 48%) than those with gains only (n=3, 11%). Losses were more numerous than gains (44/20 vs. 14/10). Single aberrations were seen in seven patients. Five of these were deletions affecting 9p21.3, two were gains in 21q. In the 27 cases, the most commonly detected aberrations were deletions involving 9p21.3 (n=10), 5/10 (50%) being T-ALL. In all the 10 cases the CDKN2A gene was affected. Other aberrations seen more than once were deletion of 6q (n=4), amplification of the terminal part of 21q (n=3), amplification of 1q (n=2), deletion of 12p (n=2), deletion in 12q23-q24 (n=2), deletion in 16q22 (n=2), deletion in 17q11 (n=2) and deletion in 22q11 (n=2). Nineteen relatively small aberrations (about 2 Mb or less in size) were detected in 15 cases and such deletion was found to be the only aberration in 4/15 cases. Our data indicate that a subgroup of ALL with fully normal cytogenetics may not exist. Microarray CGH shows a clear benefit in more detailed examination of the blast cell DNA. In 85% (23/27) of the patients with initially normal karyotypes we determined single or multiple aberrations with array CGH. Losses were more frequent than gains. Seven patients (26%) had only a single aberration, three of these being submicroscopic (<200 kb).We conclude that microarray CGH enables to detect molecular-genetic changes also in ALL cases having a “normal” karyotype using conventional cytogenetics. We are getting closer to the point where normal molecular-genetic findings do not exist in leukemic lymphoblasts. Figure 1. DNA copy number alterations detected with array CGH in 27 adolescent ALL patients with initially normal or failed karyotype. Vertical lines to the left and right of each chromosome represents copy number losses and gains, respectively. Figure 1. DNA copy number alterations detected with array CGH in 27 adolescent ALL patients with initially normal or failed karyotype. Vertical lines to the left and right of each chromosome represents copy number losses and gains, respectively.