Allogeneic Hematopoietic Cell Transplantation With Reduced Toxicity Conditioning for Pediatric B Lymphoid Malignancy.

BACKGROUND: Conventional conditioning regimens for children with lymphoid malignancy undergoing allogeneic hematopoietic cell transplantation (HCT) are myeloablative and involve high-dose total body irradiation (TBI). Such regimens are associated with significant late complications. OBSERVATIONS: Here, we used a reduced-toxicity conditioning regimen comprising fludarabine, cytarabine, melphalan, and low-dose TBI (FLAMEL) to treat 5 patients with lymphoid malignancy before HCT. Four patients maintained complete remission (range, 18 to 63 mo), whereas the remaining patient who had positive minimal residual disease (MRD) before HCT relapsed. CONCLUSIONS: FLAMEL might be a suitable conditioning regimen for children with lymphoid malignancy if pre-HCT MRD is negative.

ETV6::RUNX1 Acute Lymphoblastic Leukemia: how much therapy is needed for cure?

Recent trials show 5-year survival rates >95% for ETV6::RUNX1 Acute Lymphoblastic Leukemia (ALL). Since treatment has many side effects, an overview of cumulative drug doses and intensities between eight international trials is presented to characterize therapy needed for cure. A meta-analysis was performed as a comprehensive summary of survival outcomes at 5 and 10 years. For drug dose comparison in non-high risk trial arms, risk group distribution was applied to split the trials into two groups: trial group A with ~70% (range: 63.5-75%) of patients in low risk (LR) (CCLSG ALL2004, CoALL 07-03, NOPHO ALL2008, UKALL2003) and trial group B with ~45% (range: 38.7-52.7%) in LR (AIEOP-BFM ALL 2000, ALL-IC BFM ALL 2002, DCOG ALL10, JACLS ALL-02). Meta-analysis did not show evidence of heterogeneity between studies in trial group A LR and medium risk (MR) despite differences in treatment intensity. Statistical heterogeneity was present in trial group B LR and MR. Trials using higher cumulative dose and intensity of asparaginase and pulses of glucocorticoids and vincristine showed better 5-year event-free survival but similar overall survival. Based on similar outcomes between trials despite differences in therapy intensity, future trials should investigate, to what extent de-escalation is feasible for ETV6::RUNX1 ALL.

Differential impact of asparaginase discontinuation on outcomes of children with T-cell acute lymphoblastic leukemia and T-cell lymphoblastic lymphoma.

BACKGROUND: Asparaginase is essential for treating T-cell acute lymphoblastic leukemia (T-ALL). Despite the ongoing debate on whether T-ALL and T-cell lymphoblastic lymphoma (T-LBL) are the same disease entity or two distinct diseases, patients with T-LBL often receive the same or similar treatment protocols as those with T-ALL. METHODS: The outcomes of patients with or without L-asparaginase discontinuation were retrospectively analyzed among four national protocols: Japan Association of Childhood Leukemia Study (JACLS) ALL-02 and ALL-97 for T-ALL and Japanese Pediatric Leukemia/Lymphoma Study Group ALB-NHL03 and JACLS NHL-98 for T-LBL. The hazard ratio (HR) was calculated with the Cox regression model by considering L-asparaginase discontinuation as a time-dependent variable. RESULTS: In total, 199 patients with T-ALL, and 133 patients with T-LBL were included. L-asparaginase discontinuation compromised event-free survival (EFS) of T-ALL patients (ALL-02: HR 3.32, 95% confidence interval [CI] 1.40-7.90; ALL-97: HR 3.39, 95%CI 1.19-9.67). Conversely, EFS compromise was not detected among T-LBL patients (ALB-NHL03: HR 1.39, 95%CI 0.41-4.68; NHL-98: HR 0.92, 95%CI 0.11-7.60). CONCLUSION: The effects of L-asparaginase discontinuation differed between T-ALL and T-LBL. We assume that the differential impact results from (1) the inherent differential response to L-asparaginase between them and/or (2) a less stringent assessment of early treatment response in T-LBL than in T-ALL. Given the poor salvage rate of refractory or relapsed T-ALL and T-LBL, optimization of the frontline therapy is critical, and the current study provides a new suggestion for further treatment modifications. However, larger studies in contemporary intensified treatment protocols are required.

Biologic and clinical analysis of childhood gamma delta T-ALL identifies LMO2/STAG2 rearrangements as extremely high-risk.

Acute lymphoblastic leukemia expressing the gamma delta T cell receptor (yo T-ALL) is a poorly understood disease. We studied 200 children with yo T-ALL from 13 clinical study groups to understand the clinical and genetic features of this disease. We found age and genetic drivers were significantly associated with outcome. yo T-ALL diagnosed in children under three years of age was extremely high-risk and enriched for genetic alterations that result in both LMO2 activation and STAG2 inactivation. Mechanistically, using patient samples and isogenic cell lines, we show that inactivation of STAG2 profoundly perturbs chromatin organization by altering enhancer-promoter looping, resulting in deregulation of gene expression associated with T-cell differentiation. High throughput drug screening identified a vulnerability in DNA repair pathways arising from STAG2 inactivation, which can be targeted by Poly(ADP-ribose) polymerase (PARP) inhibition. These data provide a diagnostic framework for classification and risk stratification of pediatric yo T-ALL.

Cerebellar peduncle damage in Langerhans cell histiocytosis-associated neurodegenerative disease revealed by diffusion tensor imaging.

PURPOSE: To confirm the hypothesis that brain white matter damage is involved in the pathogenesis and disease progression of Langerhans cell histiocytosis (LCH)-associated neurodegenerative disease (ND), we aimed to analyze pediatric patients with LCH using diffusion tensor imaging (DTI). METHODS: We enrolled 33 patients with LCH and obtained 33 DTI datasets. Using DTI-based tractography, fractional anisotropy (FA), apparent diffusion coefficient (ADC), axial diffusivity (AD), and radial diffusivity (RD) were measured in the cerebral and cerebellar white matter tracts. The participants were divided into three groups-non-ND, ND without clinical symptoms (r-ND), and ND with clinical symptoms (c-ND)-according to their clinical status during the examination with DTI. We compared the DTI parameters in white matter tracts were compared among the three groups. RESULTS: In the order of non-ND, r-ND, and c-ND groups, the FA in superior cerebellar peduncle (SCP) and middle cerebellar peduncle (MCP) significantly decreased, the ADC, AD, and RD of MCP, and the RD of SCP were significantly elevated (FA-SCP; p < 0.001, FA-MCP; p = 0.026, ADC-MCP; p < 0.001, AD-MCP; p = 0.002, RD-MCP; p = 0.003, and RD-SCP; p = 0.018). Furthermore, in the simple linear regression analysis, the FA, ADC, AD, and RD values in the MCP and the FA value in the SCP were significantly influenced by the presence of neurological symptoms and ND findings on MRI (all p < 0.001). CONCLUSION: In LCH-ND, we identified microstructural damage in the SCP and MCP. DTI parameters in these tracts may help monitor LCH-ND; therefore, future studies are required to validate these results in a large cohort.

Reduced-intensity allogenic transplantation for children and adolescents with Philadelphia chromosome-positive acute lymphoblastic leukemia.

Survival rates of patients with Philadelphia chromosome-positive ALL (Ph+ALL) have improved considerably with the introduction of tyrosine kinase inhibitors (TKI); however, hematopoietic stem cell transplantation (HSCT) continues to play an important role. Reduced-intensity conditioning (RIC) regimens have been widely applied particularly for older patients, but their validity for children and adolescents with Ph+ALL has not been investigated. In this study, data from patients receiving HSCT for de novo Ph+ALL in first or second remission at ages younger than 25 years and with a history of pre-HSCT TKI therapy were retrospectively collected through the nationwide registry in Japan. In 265 patients who received myeloablative conditioning (MAC) and 33 patients receiving RIC, 5-year leukemia-free survival (LFS) rates were 67.3% and 79.8%, respectively (p = 0.142). Multivariate analysis of LFS, focusing on patients with good performance status, identified RIC as a significant prognostic factor for LFS (hazard ratio 0.32, p = 0.032), as well as older age, higher leukocyte count at diagnosis, and disease with additional chromosomal abnormalities. These trends were similar when we focused on patients who received prophylactic post-HSCT TKI treatment, as 5-year LFS was 81.0% for MAC and 84.4% for RIC (p = 0.748). In summary, HSCT with RIC regimen showed at least comparable LFS to HSCT with MAC regimen, and RIC was an independent favorable prognostic factor on multivariate analysis adjusting potential prognostic factors. While patient numbers were limited, our data suggest that RIC may be safely applied in this group, particularly combined with prophylactic post-HSCT TKI maintenance therapy.

RNA-seq-based miRNA signature as an independent predictor of relapse in pediatric B-cell acute lymphoblastic leukemia.

ABSTRACT: Aberrant micro-RNA (miRNA) expression profiles have been associated with disease progression and clinical outcome in pediatric cancers. However, few studies have analyzed genome-wide dysregulation of miRNAs and messenger RNAs (mRNAs) in pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL). To identify novel prognostic factors, we comprehensively investigated miRNA and mRNA sequencing (miRNA-seq and mRNA-seq) data in pediatric BCP-ALL samples with poor outcome. We analyzed 180 patients, including 43 matched pairs at diagnosis and relapse. Consensus clustering of miRNA expression data revealed a distinct profile characterized by mainly downregulation of miRNAs (referred to as an miR-low cluster [MLC]). The MLC profile was not associated with any known genetic subgroups. Intriguingly, patients classified as MLC had significantly shorter event-free survival (median 21 vs 33 months; log-rank P = 3 ×10-5). Furthermore, this poor prognosis was retained even in hyperdiploid ALL. This poor prognostic MLC profiling was confirmed in the validation cohort. Notably, non-MLC profiling at diagnosis (n = 9 of 23; Fisher exact test, P = .039) often changed into MLC profiling at relapse for the same patient. Integrated analysis of miRNA-seq and mRNA-seq data revealed that the transcriptional profile of MLC was characterized by enrichment of MYC target and oxidative phosphorylation genes, reduced intron retention, and low expression of DICER1. Thus, our miRNA-mRNA integration approach yielded a truly unbiased molecular stratification of pediatric BCP-ALL cases based on a novel prognostic miRNA signature, which may lead to better clinical outcomes.

Myeloid/natural killer (NK) cell precursor acute leukemia as a distinct leukemia type.

Myeloid/natural killer (NK) cell precursor acute leukemia (MNKPL) has been described on the basis of its unique immunophenotype and clinical phenotype. However, there is no consensus on the characteristics for identifying this disease type because of its rarity and lack of defined distinctive molecular characteristics. In this study, multiomics analysis revealed that MNKPL is distinct from acute myeloid leukemia, T cell acute lymphoblastic leukemia, and mixed-phenotype acute leukemia (MPAL), and NOTCH1 and RUNX3 activation and BCL11B down-regulation are hallmarks of MNKPL. Although NK cells have been classically considered to be lymphoid lineage-derived, the results of our single-cell analysis using MNKPL cells suggest that NK cells and myeloid cells share common progenitor cells. Treatment outcomes for MNKPL are unsatisfactory, even when hematopoietic cell transplantation is performed. Multiomics analysis and in vitro drug sensitivity assays revealed increased sensitivity to l-asparaginase and reduced levels of asparagine synthetase (ASNS), supporting the clinically observed effectiveness of l-asparaginase.

Leukaemic cells expressing ETV6::FRK are sensitive to dasatinib in vivo.

ETV6::Fyn-related kinase (FRK), which is a Src family tyrosine-kinase-related fusion gene and firstly identified in our patient with paediatric high risk B cell precursor acute lymphoblastic leukaemia (B-ALL), has no evidence of efficacy of tyrosine kinase inhibitor in vivo. We performed functional analysis of ETV6::FRK to establish molecular targeting therapy and determined that dasatinib could abrogate proliferation activity of ETV6::FRK through the repression of FRK-STAT3/STAT5 pathway in vitro and significantly extended the survival time of the xenografted mice in vivo (p < 0.01). Our data support the potential of dasatinib as a therapeutic option for patients with B-ALL harboring FRK rearrangements.

Outcome of hematopoietic stem cell transplantation in pediatric patients with acute lymphoblastic leukemia not in remission enrolled in JACLS ALL-02.

Hematopoietic stem cell transplantation (HSCT) is only indicated for acute lymphoblastic leukemia (ALL) patients for whom other treatments are unlikely to be curative. However, outcomes of patients not in complete remission (CR) at HSCT remain very poor. To improve the outcomes of patients receiving HSCT, it is important to obtain detailed clinical information about patients with ALL receiving HSCT in CR and not in CR. Patients enrolled in the Japan Association of Childhood Leukemia Study ALL-02 who underwent HSCT and were not in CR (non-CR patients, n = 55) were examined. The 1-year overall survival (OS) rate of non-CR patients was 27.3%. Compared with CR patients, non-CR patients experienced very early and early relapse significantly more frequently and had poorer prognostic factors. Most interestingly, high hyperdiploid (HHD) patients showed an excellent 1-year OS of 80%. In addition, long-term survival among surviving HHD patients was longer than 5 years. All eight patients who survived after undergoing HSCT while not in CR were younger than 10 years at initial diagnosis and were negative for central nervous system involvement. While limited, these results suggest that a subset of patients may benefit from HSCT while not in CR.

Nelarabine, intensive L-asparaginase, and protracted intrathecal therapy for newly diagnosed T-cell acute lymphoblastic leukaemia in children and young adults (ALL-T11): a nationwide, multicenter, phase 2 trial including randomisation in the very high-risk group.

BACKGROUND: T-cell acute lymphoblastic leukaemia has distinct biological characteristics and a poorer prognosis than B-cell precursor acute lymphoblastic leukaemia. This trial aimed to reduce the rate of radiation and haematopoietic stem-cell transplantation (HSCT) while improving outcomes by adding nelarabine, intensified L-asparaginase, and protracted intrathecal therapy in the Berlin-Frankfurt-Münster (BFM)-type treatment. METHODS: In this nationwide, multicenter, phase 2 trial, we enrolled patients with newly diagnosed T-cell acute lymphoblastic leukaemia (age <25 years at diagnosis) conducted by Japan Children's Cancer Group and Japan Adult Leukemia Study Group. Patients were stratified into standard-risk, high-risk, and very-high-risk groups according to prednisolone response, CNS status, and end-of-consolidation minimal residual disease. We used the Associazione Italiana di Ematologia Oncologia Pediatrica (AIEOP)-BFM-ALL 2000-backbone chemotherapy. Nelarabine (650 mg/m2 per day for 5 days) was given to high-risk and very high-risk patients. All patients received, until the measurement of end-of-consolidation minimal residual disease, an identical therapy schedule, which included the prednisolone pre-phase remission induction therapy with dexamethasone (10 mg/m2 per day, for 3 weeks [for patients <10 years] or for 2 weeks including a 7-day off interval [for patients ≥10 years]) instead of prednisolone, and consolidation therapy added with Escherichia coli-derived L-asparaginase. On the basis of the stratification, patients received different intensities of treatment; L-asparaginase-intensified standard BFM-type therapy for standard risk and nelarabine-added high risk BFM-type therapy for high risk. In the very high-risk group, patients were randomly assigned (1:1) to group A (BFM-based block therapy) and group B (another block therapy, including high-dose dexamethasone) stratified by hospital, age (≥18 years or <18 years), and end-of-induction bone marrow blast percentage of M1 (<5%) or M2 (≥5%, <25%)+M3 (≥25%). Cranial radiotherapy was limited to patients with overt CNS disease at diagnosis (CNS3; >5 white blood cells per µL with blasts) and patients with no evidence of CNS disease received protracted triple intrathecal therapy. Only very high-risk patients were scheduled to receive HSCT. The primary endpoint was 3-year event-free survival for the entire cohort and the proportion of patients with disappearance of minimal residual disease between randomly assigned groups A and B in the very high-risk group. Secondary endpoints were overall survival, remission induction rate, and occurrence of adverse events. 3 years after the completion of patient accrual, a primary efficacy analysis was performed in the full analysis set and the per-protocol set. This study is registered with the Japan Registry of Clinical Trials, jRCTs041180145. FINDINGS: Between Dec 1, 2011, and Nov 30, 2017, of 349 eligible patients (median age 9 years [IQR 6-13]), 238 (68%) were male, and 28 (8%) patients had CNS3 status. 168 (48%) patients were stratified as standard risk, 103 (30%) as high risk, 39 (11%) as very high risk, and 39 (11%) as no risk (patients who had off protocol treatment before risk assessment. The composite complete remission (complete remission plus complete remission in suppression) rate after remission induction therapy was 89% (298 of 335 patients). HSCT was performed in 35 (10%) of 333 patients. With a median follow-up of 5·2 years (IQR 3·6-6·7), 3-year event-free survival was 86·4% (95% CI 82·3-89·7%) and 3-year overall survival was 91·3% (87·7-93·8%). The proportion of minimal residual disease disappearance was 0·86 (12 of 14 patients; 95% CI 0·57-0·98) in group A and 0·50 (6 of 12 patients, 0·21-0·79) in group B. Grade 3 peripheral motor neuropathy was seen in 11 (3%) of 349 patients and sensory neuropathy was seen in 6 (2%) patients. The most common grade 3 or worse adverse event was febrile neutropenia (294 [84%] of 349 patients). Treatment-related death occurred in three patients due to sepsis, gastric perforation, or intracranial haemorrhage during remission induction. INTERPRETATION: The ALL-T11 protocol produced encouraging outcomes with acceptable toxicities despite limited cranial radiotherapy and HSCT use. FUNDING: Ministry of Health, Labor and Welfare of Japan, and Japan Agency for Medical Research and Development. TRANSLATION: For the Japanese translation of the abstract see Supplementary Materials section.

The Nup98::Nsd1 fusion gene induces CD123 expression in 32D cells.

The NUP98::NSD1 fusion gene is associated with extremely poor prognosis in patients with acute myeloid leukemia (AML). NUP98::NSD1 induces self-renewal and blocks differentiation of hematopoietic stem cells, leading to development of leukemia. Despite its association with poor prognosis, targeted therapy for NUP98::NSD1-positive AML is lacking, as the details of NUP98::NSD1 function are unknown. Here, we generated 32D cells (a murine interleukin-3 (IL-3)-dependent myeloid progenitor cell line) expressing mouse Nup98::Nsd1 to explore the function of NUP98::NSD1 in AML, including comprehensive gene expression analysis. We identified two properties of Nup98::Nsd1 + 32D cells in vitro. First, Nup98::Nsd1 promoted blocking of AML cell differentiation, consistent with a previous report. Second, Nup98::Nsd1 increased dependence on IL-3 for cell proliferation, due to overexpression of the alpha subunit of the IL-3 receptor (IL3-RA, also known as CD123). Consistent with our in vitro data, IL3-RA was also upregulated in samples from patients with NUP98::NSD1-positive AML. These results highlight CD123 as a potential new therapeutic target in NUP98::NSD1-positive AML.

Prevalence of pathogenic variants in cancer-predisposing genes in second cancer after childhood solid cancers.

BACKGROUND: Second malignant neoplasms (SMNs) are one of the most severe late complications after pediatric cancer treatment. However, the effect of genetic variation on SMNs remains unclear. In this study, we revealed germline genetic factors that contribute to the development of SMNs after treatment of pediatric solid tumors. METHODS: We performed whole-exome sequencing in 14 pediatric patients with SMNs, including three brain tumors. RESULTS: Our analysis revealed that five of 14 (35.7%) patients had pathogenic germline variants in cancer-predisposing genes (CPGs), which was significantly higher than in the control cohort (p < 0.01). The identified genes with variants were TP53 (n = 2), DICER1 (n = 1), PMS2 (n = 1), and PTCH1 (n = 1). In terms of the type of subsequent cancer, leukemia and multiple episodes of SMN had an exceptionally high rate of CPG pathogenic variants. None of the patients with germline variants had a family history of SMN development. Mutational signature analysis showed that platinum drugs contributed to the development of SMN in three cases, which suggests the role of platinum agents in SMN development. CONCLUSIONS: We highlight that overlapping effects of genetic background and primary cancer treatment contribute to the development of second cancers after treatment of pediatric solid tumors. A comprehensive analysis of germline and tumor samples may be useful to predict the risk of secondary cancers.

Outcomes following induction failure in Japanese children with acute lymphoblastic leukemia.

The characteristics and prognosis of Japanese children with acute lymphoblastic leukemia (ALL) who fail to achieve complete remission after remission induction chemotherapy (i.e., experience induction failure) are poorly understood. Therefore, we retrospectively analyzed data of patients enrolled in Japanese clinical trials for newly diagnosed ALL between 1996 and 2009. Among 4956 participants, 89 (1.8%) experienced induction failure. With a 6.0-year median follow-up, the 5-year overall survival rate of the entire cohort was 43.0% ± 5.5%. Survival rates did not differ between patients with B-cell precursor ALL (BCP-ALL) and T-cell ALL (T-ALL). In multivariate analysis, day 15 M3 marrow (bone marrow blast count ≥ 25%) was significantly correlated with poorer survival in the whole or BCP-ALL cohorts. In T-ALL, age < 6 years was significantly associated with poor survival. However, due to the small sample size, this correlation must be further investigated. Most T-ALL and BCR-ABL-positive BCP-ALL patients underwent allogeneic stem cell transplantation (allo-SCT). Survival rates did not differ between BCR-ABL-negative BCP-ALL patients who did and did not undergo allo-SCT, possibly due to the inclusion of lower-risk patients in the latter group. In conclusion, the induction failure rate and survival after diagnosis of induction failure in our study were comparable to previously reported figures.

Impact of asparaginase discontinuation on outcomes of children with acute lymphoblastic leukaemia receiving the Japan Association of Childhood Leukaemia Study ALL-02 protocol.

Asparaginase is an essential drug for acute lymphoblastic leukaemia (ALL) treatment, but has several side effects, and its discontinuation often compromises patient outcomes. In the prospective Japan Association of Childhood Leukaemia Study ALL-02 protocol, two major changes were made: (1) additional chemotherapies to compensate for the reduction of treatment intensity when asparaginase was discontinued and (2) more intensive concomitant corticosteroid administration, relative to our previous ALL-97 protocol. In ALL-02 study, 1192 patients were included and L-asparaginase was discontinued for 88 (7.4%). Discontinuation due to allergy was markedly decreased relative to the ALL-97 protocol (2.3% vs 15.4%). Event-free survival (EFS) among patients with T-ALL was compromised when L-asparaginase was discontinued, as well as among patients with high-risk B-cell ALL, especially when discontinued before maintenance therapy. Moreover, multivariate analysis identified discontinuation of L-asparaginase as an independent poor prognostic factor for EFS. In the current study, additional chemotherapies failed to fully compensate for L-asparaginase discontinuation, illustrating the difficulty of replacing asparaginase with other classes of drugs, although this study was not designed to evaluate the effect of these modifications. Concomitant intensive corticosteroid treatment may help to reduce allergy to asparaginase. These results will assist in further optimization of asparaginase use.

Intensification of treatment with vinca alkaloid does not improve outcomes in pediatric patients with Langerhans cell histiocytosis: results from the JPLSG LCH-12 study.

Chemotherapy with cytarabine, vincristine (VCR), and prednisolone has achieved low mortality rates in pediatric patients with Langerhans cell histiocytosis (LCH). However, relapse rates remain high, making event-free survival (EFS) rates unsatisfactory. A nationwide clinical trial, LCH-12, tested a modified protocol in which the early maintenance phase was intensified with increasing dosages of VCR. Patients newly diagnosed with multifocal bone (MFB) or multisystem (MS) LCH and aged < 20 years at diagnosis were enrolled between June 2012 and November 2017. Of the 150 eligible patients, 43 with MFB were treated for 30 weeks and 107 with MS LCH were treated for 54 weeks. One patient with MS LCH died of sepsis during the induction phase. The 3-year EFS rates among patients with MFB LCH, risk organ (RO)-negative MS LCH, and RO-positive MS LCH were 66.7% (95% confidential interval [CI], 56.5-77.0%), 66.1% (95% CI 52.9-76.4%), and 51.1% (95% CI 35.8-64.5%), respectively, similar to previously observed rates. EFS rates were significantly lower in patients with disease activity scores > 6 than in those with scores ≤ 6. The strategy that included more intense treatment with VCR was not effective. Other strategies are required to improve outcomes in patients with pediatric LCH.

Guest editorial: recent progress in pediatric leukemia.

Recent progress in comprehensive genomic analysis and well-designed clinical trials has dramatically improved the treatment strategies for pediatric leukemia, resulting in better prognosis and reducing acute and late adverse events. This review series describes successes and challenges for the future in the management of pediatric leukemia.

Relapses of multisystem/multifocal bone Langerhans cell histiocytosis in paediatric patients: Data analysis from the JLSG-96/02 study.

We assessed relapse patterns in paediatric patients with relapsed Langerhans cell histiocytosis (LCH) who were initially treated with the JLSG-96/02 protocol. We analysed 187 relapse events in 101 relapsed LCH patients [31 with multifocal bone (MFB) and 70 with multisystem (MS) at LCH diagnosis] among a total 317 patients enrolled in JLSG-96/-02 studies. Relapse of LCH was defined as an exacerbation of the non-active disease (NAD) condition. Of the 317 patients, 101 (31.9%) had the first relapse at 1.5 years after initiation of therapy. The first relapse and subsequent relapses did not differ between patients with MFB and MS disease. Of the 187 relapse events, relapse occurred as a single-system disease (n = 159; 85%), in which isolated bone relapse (n = 104; 55%) was the most common. Relapse at MS disease with the risk of organ involvement is extremely rare. After relapse(s), most patients underwent chemotherapy (122/187; 65%) and 87% of them achieved NAD status again. The incidence of permanent consequences was significantly higher in patients with relapses than in those without relapses. In the JLSG cohort, bone relapse most occurred in both MFB and MS patients. Most relapses could be effectively controlled by repeated administration of the initial chemotherapy.