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Oncogenic subtypes in childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL) are used for risk stratification. However, a significant number of BCP-ALL patients are still genetically unassigned. Using array-comparative genomic hybridization in a selected BCP-ALL cohort, we characterized a recurrent V(D)J-mediated intragenic deletion of the ERG gene (ERG(del)). A breakpoint-specific PCR assay was designed and used to screen an independent non-selected cohort of 897 children aged 1-17 years treated for BCP-ALL in the EORTC-CLG 58951 trial. ERG(del) was found in 29/897 patients (3.2%) and was mutually exclusive of known classifying genetic lesions, suggesting that it characterized a distinct leukemia entity. ERG(del) was associated with higher age (median 7.0 vs. 4.0 years, P=0.004), aberrant CD2 expression (43.5% vs. 3.7%, P<0.001) and frequent IKZF1 Δ4-7 deletions (37.9% vs. 5.3%, P<0.001). However, ERG(del) patients had a very good outcome, with an 8-year event-free survival (8-y EFS) and an 8-year overall survival of 86.4% and 95.6%, respectively, suggesting that the IKZF1 deletion had no impact on prognosis in this genetic subtype. Accordingly, within patients with an IKZF1 Δ4-7 deletion, those with ERG(del) had a better outcome (8-y EFS: 85.7% vs. 51.3%; hazard ratio: 0.16; 95% confidence interval: 0.02-1.20; P=0.04). These findings have implications for further stratification including IKZF1 status.

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Risk-adjusted treatment stratification in T-cell acute lymphoblastic leukemias (T-ALLs) is currently based only on early response to chemotherapy. We investigated the prognostic implication of hyperactivation of NOTCH pathway resulting from mutations of NOTCH1 or FBXW7 in children with T-ALL enrolled in EORTC-CLG trials. Overall, 80 out of 134 (60%) patients were NOTCH þ (NOTCH1 and/or FBXW7 mutated). Although clinical presentations were not significantly associated with NOTCH status, NOTCH þ patients showed a better early response to chemotherapy as compared with NOTCHÀ patients, according to the rate of poor pre-phase 'responders' (25% versus 44%; P ¼ 0.02) and the incidence of high minimal residual disease (MRD) levels (11% (7/62) versus 32% (10/31); P ¼ 0.01) at completion of induction. However, the outcome of NOTCH þ patients was similar to that of NOTCHÀ patients, with a 5-year event-free survival (EFS) of 73% and 70% (P ¼ 0.82), and 5-year overall survival of 82% and 79% (P ¼ 0.62), respectively. In patients with high MRD levels, the 5-year EFS rate was 0% (NOTCH þ ) versus 42% (NOTCHÀ), whereas in those with low MRD levels, the outcome was similar: 76% (NOTCH þ ) versus 78% (NOTCHÀ). The incidence of isolated central nervous system (CNS) relapses was relatively high in NOTCH1 þ patients (8.3%), which could be related to a higher propensity of NOTCH þ leukemic blasts to target the CNS.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• The pharmacogenetic polymorphisms of both TPMT and ITPA are associated with individual variability in 6-mercaptopurine (6-MP) intracellular metabolism.• The balance between red blood cell (RBC) 6-thioguanine nucleotide (6TGN) and 6-methylated metabolite (6-MMPN) concentrations has an important impact on efficacy in children treated for acute lymphoblastic leukemia.• Hepatotoxicity is a frequent complication of the association 6-MP and methotrexate during maintenance therapy. WHAT THIS STUDY ADDS• RBC 6-TGN concentrations are dependant on TPMT genotype and age, while RBC 6-MMPN concentrations depend on TPMT and ITPA polymorphisms. • Children aged 6 years or less had lower RBC 6-TGN concentrations during maintenance therapy, demonstrating an age effect on 6-MP intracellular metabolism.• Hepatotoxicity is a frequent complication of the association of 6-MP and methotrexate. A 6-MMPN threshold of 5000 pmol/8 ¥ 10 8 RBC was associated with an increased risk of hepatotoxicity. AIMS6-mercaptopurine (6-MP) is used in the treatment of childhood acute lymphoblastic leukaemia (ALL). Its red blood cell (RBC) metabolite concentrations (6-thioguanine [6-TGN] and 6-methylmercaptopurine nucleotides ) are related to drug response. We investigated the impact of non-genetic covariates and pharmacogenetic polymorphisms affecting thiopurine methyltransferase (TPMT) and inosine triphosphate pyrophosphatase (ITPA) on 6-MP metabolism and response. METHODSSixty-six children with ALL treated according to EORTC 58951 protocol were included in this study. Six patients had a heterozygous genotype for the most common TPMT polymorphisms, nine for ITPA 94 C > A and 17 for ITPA IVS2 + 21 A > C. 6-MP metabolites concentrations were analyzed by mixed model analysis. RESULTSDuring maintenance, steady-state RBC 6-TGN concentrations were lower in patients aged 6 years or younger ( CONCLUSIONIn this study, age and both TPMT and ITPA genotypes influenced 6-MP metabolism. High 6-MMPN was associated with hepatotoxicity. These pharmacological tools should be used to monitor ALL treatment in children.

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The added value of IKZF1 gene deletion (IKZF1(del)) as a stratifying criterion in B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is still debated. We performed a comprehensive analysis of the impact of IKZF1(del) in a large cohort of children (n=1223) with BCR-ABL1-negative BCP-ALL treated in the EORTC-CLG trial 58951. Patients with IKZF1(del) had a lower 8-year event-free survival (EFS, 67.7% versus 86.5%; hazard ratio (HR)=2.41; 95% confidence interval (CI)=1.75-3.32; P<0.001). Importantly, despite association with high-risk features such as high minimal residual disease, IKZF1(del) remained significantly predictive in multivariate analyses. Analysis by genetic subtype showed that IKZF1(del) increased risk only in the high hyperdiploid ALLs (HR=2.57; 95% CI=1.19-5.55; P=0.013) and in 'B-other' ALLs, that is, lacking classifying genetic lesions (HR=2.22; 95% CI=1.45-3.39; P<0.001), the latter having then a dramatically low 8-year EFS (56.4; 95% CI=44.6-66.7). Among IKZF1(del)-positive patients randomized for vincristine-steroid pulses during maintenance, those receiving pulses had a significantly higher 8-year EFS (93.3; 95% CI=61.3-99.0 versus 42.1; 95% CI=20.4-62.5). Thus, IKZF1(del) retains independent prognostic significance in the context of current risk-adapted protocols, and is associated with a dismal outcome in 'B-other' ALL. Addition of vincristine-steroid pulses during maintenance may specifically benefit to IKZF1(del) patients in preventing relapses.

We conclude that PCV7 vaccination at 3 months after stem cell transplantation is not inferior to PCV7 vaccination at 9 months after transplantation. Because invasive pneumococcal disease can occur early, we recommend starting the PCV7 vaccination series at 3 months after transplantation to ensure earlier protection against Streptococcus pneumoniae. However, the early vaccination may result in only short-lasting response and may not prime for a 23-valent pneumococcal polysaccharide vaccine boost as efficiently as the late vaccination.