Outcomes of treatment for relapsed acute lymphoblastic leukaemia in children with Down syndrome

INSPIRED Symposium Part 4A: Access to CAR T Cell Therapy in Unique Populations with B Cell Acute Lymphoblastic Leukemia

The approval of tisagenlecleucel (tisa-cel) for use in children with B cell acute lymphoblastic leukemia (B-ALL) was based on the phase 2 ELIANA trial, a global registration study. However, the ELIANA trial excluded specific subsets of patients facing unique challenges and did not include a sufficient number of patients to adequately evaluate outcomes in rare subpopulations. Since the commercialization of tisa-cel, data have become available that support therapeutic indications beyond the specific cohorts previously eligible for chimeric antigen receptor (CAR) T cells targeted to CD19 (CD19 CAR-T) therapy on the registration clinical trial. Substantial real-world data and aggregate clinical trial data have addressed gaps in our understanding of response rates, longer-term efficacy, and toxicities associated with CD19 CAR-T in special populations and rare clinical scenarios. These include patients with central nervous system relapsed disease, who were excluded from ELIANA and other early CAR-T trials owing to concerns about risk of neurotoxicity that have not been born out. There is also interest in the use of CD19 CAR-T for very-high-risk patients earlier in the course of therapy, such as patients with persistent minimal residual disease after 2 cycles of upfront chemotherapy and patients with first relapse of B-ALL. However, these indications are not specified on the label for tisa-cel and historically were not included in eligibility criteria for most clinical trials; data addressing these populations are needed. Populations at high risk of relapse, including patients with high-risk cytogenetic lesions, infants with B-ALL, patients with trisomy 21, and young adults with B-ALL, also may benefit from earlier treatment with CD19 CAR-T. It is important to prospectively study patient-reported outcomes given the differential toxicity expected between CD19 CAR-T and the historic standard of care, hematopoietic cell transplantation. Now that CD19 CAR-T therapy is commercially available, studies evaluating potential access disparities created by this very expensive novel therapy are increasingly pressing.

Six Years of Disease-free Survival After a Second Cord Blood Transplantation for Recurrent Acute Lymphocytic Leukemia in a Child With Down Syndrome

Outcomes are extremely poor in Down syndrome-associated acute lymphocytic leukemia, particularly in recurrent cases. A 2-year-old boy with Down syndrome-associated acute lymphocytic leukemia achieved complete remission after standard chemotherapy. However, he experienced recurrence twice in the bone marrow and central nervous system. Salvage treatments included whole-brain/whole-spine irradiation. Thereafter, the patient received a second cord blood transplantation after the reduced-intensity conditioning. The graft was characterized by killer cell immunoglobulin-like receptor ligands mismatch. The patient has subsequently survived for 6.5 years without recurrence. We speculate that killer cell immunoglobulin-like receptor ligand-mismatched cord blood transplantation enhanced the graft-versus-leukemia effect through natural killer cells, and conferred long-term remission.

Gain of chromosome 21 increases the propensity for P2RY8::CRLF2 acute lymphoblastic leukemia via increased HMGN1 expression

Acute lymphoblastic leukemia (ALL) patients with a gain of chromosome 21, intrachromosomal amplification of chromosome 21 (iAMP21), or Down syndrome (DS), have increased expression of genes in the DS critical region (DSCR) of chromosome 21, including the high-mobility group nucleosome-binding protein 1, HMGN1. Children with DS are predisposed to develop hematologic malignancies, providing insight into the role of chromosome 21 in the development of leukemias. A 320-kb deletion in the pseudoautosomal region of the X/Y chromosome in leukemic cells, resulting in a gene fusion between the purinergic receptor and cytokine receptor-like factor-2 (P2Y Receptor Family Member 8 (P2RY8)::CRLF2), is a common feature in ~60% of DS-ALL and ~40% of iAMP21 patients, suggesting a link between chromosome 21 and P2RY8::CRLF2. In an Australian cohort of pediatric B-ALL patients with P2RY8::CRLF2 (n = 38), eight patients harbored gain of chromosome 21 (+21), and two patients had iAMP21, resulting in a significantly increased HMGN1 expression. An inducible CRISPR/Cas9 system was used to model P2RY8::CRLF2 and investigate its cooperation with HMGN1. This model was then used to validate HMGN1 as an influencing factor for P2RY8::CRLF2 development. Using Cas9 to cleave the DNA at the pseudoautosomal region without directed repair, cells expressing HMGN1 favored repair, resulting in P2RY8::CRLF2 generation, compared with cells without HMGN1. CRISPR/Cas9 P2RY8::CRLF2 cells expressing HMGN1 exhibit increased proliferation, thymic stromal lymphopoietin receptor (TSLPR) expression, and JAK/STAT signaling, consistent with cells from patients with P2RY8::CRLF2. Our patient expression data and unique CRISPR/Cas9 modeling, when taken together, suggest that HMGN1 increases the propensity for P2RY8::CRLF2 development. This has important implications for patients with DS, +21, or iAMP21.

How I use risk factors for success or failure of CD19 CAR T cells to guide management of children and AYA with B-cell ALL

By overcoming chemotherapeutic resistance, chimeric antigen receptor (CAR) T cells facilitate deep, complete remissions and offer the potential for long-term cure in a substantial fraction of patients with chemotherapy refractory disease. However, that success is tempered with 10% to 30% of patients not achieving remission and over half of patients treated eventually experiencing relapse. With over a decade of experience using CAR T cells in children, adolescents, and young adults (AYA) to treat relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL) and 5 years since the first US Food and Drug Administration approval, data defining the nuances of patient-specific risk factors are emerging. With the commercial availability of 2 unique CD19 CAR T-cell constructs for B-ALL, in this article, we review the current literature, outline our approach to patients, and discuss how individual factors inform strategies to optimize outcomes in children and AYA receiving CD19 CAR T cells. We include data from both prospective and recent large retrospective studies that offer insight into understanding when the risks of CAR T-cell therapy failure are high and offer perspectives suggesting when consolidative hematopoietic cell transplantation or experimental CAR T-cell and/or alternative immunotherapy should be considered. We also propose areas where prospective trials addressing the optimal use of CAR T-cell therapy are needed.

HMGN1 plays a significant role in CRLF2 driven Down Syndrome leukemia and provides a potential therapeutic target in this high-risk cohort

The genetic basis of the predisposition for Down Syndrome (DS) patients to develop cytokine receptor-like factor 2 rearranged (CRLF2r) acute lymphoblastic leukemia (ALL) is currently unknown. Genes located on chromosome 21 and expressed in hematopoietic cells are likely candidates for investigation of CRLF2r DS-ALL pathogenesis. We explored the high-mobility group nucleosome-binding protein 1 (HMGN1), located in the DS critical region, in an inducible CRISPR/Cas9 knockout (KO) xenograft model to assess the effect of HMGN1 loss of function on the leukemic burden. We demonstrated HMGN1 KO-mitigated leukemic phenotypes including hepatosplenomegaly, thrombocytopenia, and anemia, commonly observed in leukemia patients, and significantly increased survival in vivo. HMGN1 overexpression in murine stem cells and Ba/F3 cells in vitro, in combination with P2RY8-CRLF2, resulted in cytokine-independent transformation and upregulation of cell signaling pathways associated with leukemic development. Finally, in vitro screening demonstrated successful targeting of P2RY8-CRLF2 and HMGN1 co-expressing cell lines and patient samples with fedratinib (JAK2 inhibitor), and GSK-J4 (demethylase inhibitor) in combination. Together, these data provide critical insight into the development and persistence of CRLF2r DS-ALL and identify HMGN1 as a potential therapeutic target to improve outcomes and reduce toxicity in this high-risk cohort of young patients.

Allogeneic Hematopoietic Stem Cell Transplantation for Children With Acute Lymphoblastic Leukemia: Shifting Indications in the Era of Immunotherapy

Pediatric acute lymphoblastic leukemia generally carries a good prognosis, and most children will be cured and become long-term survivors. However, a portion of children will harbor high-risk features at the time of diagnosis, have a poor response to upfront therapy, or suffer relapse necessitating more intensive therapy, which may include allogeneic hematopoietic stem cell transplant (HSCT). Recent advances in risk stratification, improved detection and incorporation of minimal residual disease (MRD), and intensification of upfront treatment have changed the indications for HSCT over time. For children in first complete remission, HSCT is generally reserved for those with the highest risk of relapse. These include patients with unfavorable features/cytogenetics who also have a poor response to induction and consolidation chemotherapy, usually reflected by residual blasts after prednisone or by detectable MRD at pre-defined time points. In the relapsed setting, children with first relapse of B-cell ALL are further stratified for HSCT depending on the time and site of relapse, while all patients with T-cell ALL are generally consolidated with HSCT. Alternatives to HSCT have also emerged over the last decade including immunotherapy and chimeric antigen receptor (CAR) T-cell therapy. These novel agents may spare toxicity while attempting to achieve MRD-negative remission in the most refractory cases and serve as a bridge to HSCT. In some situations, these emerging therapies can indeed be curative for some children with relapsed or resistant disease, thus, obviating the need for HSCT. In this review, we seek to summarize the role of HSCT in the current era of immunotherapy.

Other (Non-CNS/Testicular) Extramedullary Localizations of Childhood Relapsed Acute Lymphoblastic Leukemia and Lymphoblastic Lymphoma-A Report from the ALL-REZ Study Group

Children with other extramedullary relapse of acute lymphoblastic leukemia are currently poorly characterized. We aim to assess the prevalence and the clinical, therapeutic and prognostic features of extramedullary localizations other than central nervous system or testis in children with relapse of acute lymphoblastic leukemia (ALL) and lymphoblastic lymphoma (LBL) treated on a relapsed ALL protocol.

PATIENTS AND METHODS

Patients with relapse of ALL and LBL, treated according to the multicentric ALL-REZ BFM trials between 1983 and 2015, were analyzed for other extramedullary relapse (OEMR) of the disease regarding clinical features, treatment and outcome. Local treatment/irradiation has been recommended on an individual basis and performed only in a minority of patients.

RESULTS

A total of 132 out of 2323 (5.6%) patients with ALL relapse presented with an OEMR (combined bone marrow relapse n = 78; isolated extramedullary relapse n = 54). Compared to the non-OEMR group, patients with OEMR had a higher rate of T-immunophenotype (p < 0.001), a higher rate of LBL (p < 0.001) and a significantly different distribution of time to relapse, i.e., more very early and late relapses compared to the non-OEMR group (p = 0.01). Ten-year probabilities of event-free survival (pEFS) and overall survival (pOS) in non-OEMR vs. OEMR were 0.38 ± 0.01 and 0.32 ± 0.04 (p = 0.0204) vs. 0.45 ± 0.01 and 0.37 ± 0.04 (p = 0.0112), respectively. OEMRs have been classified into five subgroups according to the main affected compartment: lymphatic organs (n = 32, 10y-pEFS 0.50 ± 0.09), mediastinum (n = 35, 10y-pEFS 0.11 ± 0.05), bone (n = 12, 0.17 ± 0.11), skin and glands (n = 21, 0.32 ± 0.11) and other localizations (n = 32, 0.41 ± 0.09). Patients with OEMR and T-lineage ALL/LBL showed a significantly worse 10y-pEFS (0.15 ± 0.04) than those with B-Precursor-ALL (0.49 ± 0.06, p < 0.001). Stratified into standard risk (SR) and high risk (HR) groups, pEFS and pOS of OEMR subgroups were in the expected range whereas the mediastinal subgroup had a significantly worse outcome. Subsequent relapses involved more frequently the bone marrow (58.4%) than isolated extramedullary compartments (41.7%). In multivariate Cox regression, OEMR confers an independent prognostic factor for inferior pEFS and pOS.

CONCLUSION

OEMR is adversely related to prognosis. However, the established risk classification can be applied for all subgroups except mediastinal relapses requiring treatment intensification. Generally, isolated OEMR of T-cell-origin needs an intensified treatment including allogeneic stem cell transplantation (HSCT) as a curative approach independent from time to relapse. Local therapy such as surgery and irradiation may be of benefit in selected cases. The indication needs to be clarified in further investigations.

Patient with Down syndrome and relapsed acute lymphoblastic leukemia with sustained remission despite only partial R3 chemotherapy

DS-ALL has a higher rate of relapse and treatment-related mortality. The newer immunotherapies are potentially better options. Relapsed ALL with positive MRD has a poor prognosis. Transient long-term remission after ALL relapse due to partial chemotherapy combined severe infection is rare.

Immunotherapy in Pediatric B-Cell Acute Lymphoblastic Leukemia: Advances and Ongoing Challenges

Leukemia, most commonly B-cell acute lymphoblastic leukemia (B-ALL), accounts for about 30% of childhood cancer diagnoses. While there have been dramatic improvements in childhood ALL outcomes, certain subgroups-particularly those who relapse-fare poorly. In addition, cure is associated with significant short- and long-term side effects. Given these challenges, there is great interest in novel, targeted approaches to therapy. A number of new immunotherapeutic agents have proven to be efficacious in relapsed or refractory disease and are now being investigated in frontline treatment regimens. Blinatumomab (a bispecific T-cell engager that targets cluster of differentiation [CD]-19) and inotuzumab ozogamicin (a humanized antibody-drug conjugate to CD22) have shown the most promise. Chimeric antigen receptor T (CAR-T) cells, a form of adoptive immunotherapy, rely on the transfer of genetically modified effector T cells that have the potential to persist in vivo for years, providing ongoing long-term disease control. In this article, we discuss the clinical biology and treatment of B-ALL with an emphasis on the role of immunotherapy in overcoming the challenges of conventional cytotoxic therapy. As immunotherapy continues to move into the frontline of pediatric B-ALL therapy, we also discuss strategies to address unique side effects associated with these agents and efforts to overcome mechanisms of resistance to immunotherapy.

Gain of chromosome 21 in hematological malignancies: lessons from studying leukemia in children with Down syndrome

Structural and numerical alterations of chromosome 21 are extremely common in hematological malignancies. While the functional impact of chimeric transcripts from fused chromosome 21 genes such as TEL-AML1, AML1-ETO, or FUS-ERG have been extensively studied, the role of gain of chromosome 21 remains largely unknown. Gain of chromosome 21 is a frequently occurring aberration in several types of acute leukemia and can be found in up to 35% of cases. Children with Down syndrome (DS), who harbor constitutive trisomy 21, highlight the link between gain of chromosome 21 and leukemogenesis, with an increased risk of developing acute leukemia compared with other children. Clinical outcomes for DS-associated leukemia have improved over the years through the development of uniform treatment protocols facilitated by international cooperative groups. The genetic landscape has also recently been characterized, providing an insight into the molecular pathogenesis underlying DS-associated leukemia. These studies emphasize the key role of trisomy 21 in priming a developmental stage and cellular context susceptible to transformation, and have unveiled its cooperative function with additional genetic events that occur during leukemia progression. Here, using DS-leukemia as a paradigm, we aim to integrate our current understanding of the role of trisomy 21, of critical dosage-sensitive chromosome 21 genes, and of associated mechanisms underlying the development of hematological malignancies. This review will pave the way for future investigations on the broad impact of gain of chromosome 21 in hematological cancer, with a view to discovering new vulnerabilities and develop novel targeted therapies to improve long term outcomes for DS and non-DS patients.

Cutting to the Front of the Line: Immunotherapy for Childhood Acute Lymphoblastic Leukemia

Although many children and young adults with B-cell acute lymphoblastic leukemia (B-ALL) are cured with modern, risk-adapted chemotherapy regimens, 10% to 15% of patients will experience relapse or have refractory disease. Recent efforts to further intensify cytotoxic chemotherapy regimens in the frontline setting have failed as a result of excessive toxicity or lack of improvement in efficacy. As a result, novel approaches will be required to achieve cures in more newly diagnosed patients. Multiple immune-based therapies have demonstrated considerable efficacy in the setting of relapsed or refractory (R/R) disease, including CD19 targeting with blinatumomab and tisagenlecleucel and CD22 targeting with inotuzumab ozogamicin. These agents are now under investigation by the Children's Oncology Group (COG) in clinical trials for newly diagnosed B-ALL, with integration into standard chemotherapy regimens based on clinically and biology-based risk stratification as well as disease response.

Precision medicine approaches may be the future for CRLF2 rearranged Down Syndrome Acute Lymphoblastic Leukaemia patients

Breakthrough studies over the past decade have uncovered unique gene fusions implicated in acute lymphoblastic leukaemia (ALL). The critical gene, cytokine receptor-like factor 2 (CRLF2), is rearranged in 5-16% of B-ALL, comprising 50% of Philadelphia-like ALL and cooperates with genomic lesions in the Jak, Mapk and Ras signalling pathways. Children with Down Syndrome (DS) have a predisposition to developing CRLF2 rearranged-ALL which is observed in 60% of DS-ALL patients. These patients experience a poor survival outcome. Mutations of genes involved in epigenetic regulation are more prevalent in DS-ALL patients than non-DS ALL patients, highlighting the potential for alternative treatment strategies. DS-ALL patients also suffer greater treatment-related toxicity from current ALL treatment regimens compared to non-DS-ALL patients. An increased gene dosage of critical genes on chromosome 21 which have roles in purine synthesis and folate transport may contribute. As the genomic landscape of DS-ALL patients is different to non-DS-ALL patients, targeted therapies for individual lesions may improve outcomes. Therapeutically targeting each rearrangement with targeted or combination therapy that will perturb the transforming signalling pathways will likely improve the poor survival rates of this subset of patients.

Pulmonary hemosiderosis in children with Down syndrome: a national experience

BACKGROUND

Pulmonary hemosiderosis is a rare and complex disease in children. A previous study from the French RespiRare® network led to two important findings: 20% of the children presented with both pulmonary hemosiderosis and Down syndrome (DS), and at least one tested autoantibody was found positive in 50%. This study investigates the relationships between pulmonary hemosiderosis and DS.

METHODS

Patients younger than 20 years old and followed for pulmonary hemosiderosis were retrieved from the RespiRare® database. Clinical, biological, functional, and radiological findings were collected, and DS and non-DS patients' data were compared.

RESULTS

A total of 34 patients (22 girls and 12 boys) were included, among whom nine (26%) presented with DS. The mean age at diagnosis was 4.1 ± 3.27 years old for non-DS and 2.9 ± 3.45 years old for DS patients. DS patients tended to present a more severe form of the disease with an earlier onset, more dyspnoea at diagnosis, more frequent secondary pulmonary hypertension, and an increased risk of fatal evolution.

CONCLUSIONS

DS patients have a higher risk of developing pulmonary hemosiderosis, and the disease seems to be more severe in this population. This could be due to the combination of an abnormal lung capillary bed with fragile vessels, a higher susceptibility to autoimmune lesions, and a higher risk of evolution toward pulmonary hypertension. A better screening for pulmonary hemosiderosis and a better prevention of hypoxia in DS paediatric patients may prevent a severe evolution of the disease.

Relapsed childhood acute lymphoblastic leukemia in the Nordic countries: prognostic factors, treatment and outcome

Relapse is the main reason for treatment failure in childhood acute lymphoblastic leukemia. Despite improvements in the up-front therapy, survival after relapse is still relatively poor, especially for high-risk relapses. The aims of this study were to assess outcomes following acute lymphoblastic leukemia relapse after common initial Nordic Society of Paediatric Haematology and Oncology protocol treatment; to validate currently used risk stratifications, and identify additional prognostic factors for overall survival. Altogether, 516 of 2735 patients (18.9%) relapsed between 1992 and 2011 and were included in the study. There were no statistically significant differences in outcome between the up-front protocols or between the relapse protocols used, but an improvement over time was observed. The 5-year overall survival for patients relapsing in the period 2002-2011 was 57.5±3.4%, but 44.7±3.2% (P<0.001) if relapse occurred in the period 1992-2001. Factors independently predicting mortality after relapse included short duration of first remission, bone marrow involvement, age ten years or over, unfavorable cytogenetics, and Down syndrome. T-cell immunophenotype was not an independent prognostic factor unless in combination with hyperleukocytosis at diagnosis. The outcome for early combined pre-B relapses was unexpectedly poor (5-year overall survival 38.0±10.6%), which supports the notion that these patients need further risk adjustment. Although survival outcomes have improved over time, the development of novel approaches is urgently needed to increase survival in relapsed childhood acute lymphoblastic leukemia.

Down syndrome preleukemia and leukemia

Children with Down syndrome (DS) and acute leukemias acute have unique biological, cytogenetic, and intrinsic factors that affect their treatment and outcome. Myeloid leukemia of Down syndrome (ML-DS) is associated with high event-free survival (EFS) rates and frequently preceded by a preleukemia condition, the transient abnormal hematopoiesis (TAM) present at birth. For acute lymphoblastic leukemia (ALL), their EFS and overall survival are poorer than non-DS ALL, it is important to enroll them on therapeutic trials, including relapse trials; investigate new agents that could potentially improve their leukemia-free survival; and strive to maximize the supportive care these patients need.

Outcome of transplantation for acute lymphoblastic leukemia in children with Down syndrome

We report on 27 patients with Down syndrome (DS) and acute lymphoblastic leukemia (ALL) who received allogeneic hematopoietic cell transplantation (HCT) between 2000 and 2009. Seventy-eight percent of patients received myeloablative conditioning and 52% underwent transplantation in second remission. Disease-free survival (DFS) was 24% at a median of 3 years. Post-transplant leukemic relapse was more frequent than expected for children with DS-ALL (54%) than for non-DS ALL. These data suggest leukemic relapse rather than transplant toxicity is the most important cause of treatment failure. Advancements in leukemia control are especially needed for improvement in HCT outcomes for DS-ALL.

Clinical and genetic features of pediatric acute lymphoblastic leukemia in Down syndrome in the Nordic countries

Background

Children with Down syndrome (DS) have an increased risk for acute lymphoblastic leukemia (ALL). Although previous studies have shown that DS-ALL differs clinically and genetically from non-DS-ALL, much remains to be elucidated as regards genetic and prognostic factors in DS-ALL.

Methods

To address clinical and genetic differences between DS-ALL and non-DS-ALL and to identify prognostic factors in DS-ALL, we ascertained and reviewed all 128 pediatric DS-ALL diagnosed in the Nordic countries between 1981 and 2010. Their clinical and genetic features were compared with those of the 4,647 B-cell precursor (BCP) ALL cases diagnosed during the same time period.

Results

All 128 DS-ALL were BCP ALL, comprising 2.7% of all such cases. The 5-year event-free survival (EFS) and overall survival (OS) were significantly (P = 0.026 and P = 0.003, respectively) worse for DS-ALL patients with white blood cell counts ≥50 × 10⁹/l. The age distributions varied between the DS and non-DS cases, with age peaks at 2 and 3 years, respectively; none of the DS patients had infant ALL (P = 0.029). The platelet counts were lower in the DS-ALL group (P = 0.005). Abnormal karyotypes were more common in non-DS-ALL (P < 0.0001), and there was a significant difference in the modal number distribution, with only 2% high hyperdiploid DS-ALL cases (P < 0.0001). The 5-year EFS and 5-year OS were significantly worse for DS-ALL (0.574 and 0.691, respectively) compared with non-DS-ALL (0.783 and 0.894, respectively) in the NOPHO ALL-1992/2000 protocols (P < 0.001).

Conclusions

The present study adds further support for genetic and clinical differences between DS-ALL and non-DS-ALL.

How I treat ALL in Down's syndrome: pathobiology and management

Children with Down syndrome are at high risk for developing B-cell precursor acute lymphoblastic leukemia (DS-ALL) associated with poor outcome due to both a high relapse rate and increased treatment-related mortality (TRM) from infections. Biologically, these heterogeneous leukemias are characterized by under-representation of the common cytogenetic subgroups of childhood ALL and overrepresentation of CRLF2-IL7R-JAK-STAT activating genetic aberrations. Although relapse is the major determinant of poor outcomes in this population, de-escalation of chemotherapy intensity might be feasible in the 10% to 15% DS-ALL patients with ETV6-RUNX1 or high hyperdipoidy in whom TRM is the major limiting event. As infection-associated TRM occurs during all treatment phases, including the maintenance period, increased surveillance and supportive care is required throughout therapy. Improvement in outcome will require better understanding of the causes of treatment failure and TRM, incorporation of new therapies targeting the unique biological properties of DS-ALL, and enhanced supportive care measures to reduce the risk of infection-related TRM. To facilitate these goals, an international collaboration plans to establish a prospective DS-ALL registry and develop specific supportive care recommendations for this at-risk population.

Acute lymphoblastic leukemia in children with Down syndrome: a retrospective analysis from the Ponte di Legno study group

Children with Down syndrome (DS) have an increased risk of B-cell precursor (BCP) acute lymphoblastic leukemia (ALL). The prognostic factors and outcome of DS-ALL patients treated in contemporary protocols are uncertain. We studied 653 DS-ALL patients enrolled in 16 international trials from 1995 to 2004. Non-DS BCP-ALL patients from the Dutch Child Oncology Group and Berlin-Frankfurt-Münster were reference cohorts. DS-ALL patients had a higher 8-year cumulative incidence of relapse (26% ± 2% vs 15% ± 1%, P < .001) and 2-year treatment-related mortality (TRM) (7% ± 1% vs 2.0% ± <1%, P < .0001) than non-DS patients, resulting in lower 8-year event-free survival (EFS) (64% ± 2% vs 81% ± 2%, P < .0001) and overall survival (74% ± 2% vs 89% ± 1%, P < .0001). Independent favorable prognostic factors include age <6 years (hazard ratio [HR] = 0.58, P = .002), white blood cell (WBC) count <10 × 10(9)/L (HR = 0.60, P = .005), and ETV6-RUNX1 (HR = 0.14, P = .006) for EFS and age (HR = 0.48, P < .001), ETV6-RUNX1 (HR = 0.1, P = .016) and high hyperdiploidy (HeH) (HR = 0.29, P = .04) for relapse-free survival. TRM was the major cause of death in ETV6-RUNX1 and HeH DS-ALLs. Thus, while relapse is the main contributor to poorer survival in DS-ALL, infection-associated TRM was increased in all protocol elements, unrelated to treatment phase or regimen. Future strategies to improve outcome in DS-ALL should include improved supportive care throughout therapy and reduction of therapy in newly identified good-prognosis subgroups.