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Lineage switch is a rare event at leukemic relapse. While mostly known to occur in KMT2A-rearranged infant leukemia, the underlying mechanism is yet to be depicted. This case report describes a female infant who achieved remission of KMT2A-MLLT3-rearranged acute monocytic leukemia, but 6 months thereafter, relapsed as KMT2A-MLLT3-rearranged acute lymphocytic leukemia. Whole exome sequencing of the bone marrow obtained pre-post lineage switch revealed two somatic mutations of PAX5 in the relapse sample. These two PAX5 alterations were suggested to be loss of function, thus to have played the driver role in the lineage switch from acute monocytic leukemia to acute lymphocytic leukemia.

Varicella-zoster virus (VZV) reactivation is a serious complication of hematopoietic stem cell transplantation (HSCT). Although low-dose acyclovir can prevent VZV reactivation after HSCT in adults, the efficacy of a dose of acyclovir lower than the recommended dose, such as 60-80 mg/kg/day in children, is unclear. In this study, we aimed to evaluate the incidence of VZV reactivation after HSCT during and after low-dose acyclovir administration for preventing VZV reactivation in children.This single-center retrospective study included children aged ≤15 years who received oral acyclovir (at 15 mg/kg/day) to prevent VZV reactivation after HSCT. We examined the cumulative incidence of VZV reactivation after HSCT, during and after prophylactic acyclovir administration.Fifty-three eligible patients were included in this study, of whom 37 underwent allogeneic HSCT. The median duration of prophylactic acyclovir therapy was 264 days (range: 69-1140 days). VZV reactivation occurred in 13 patients (24.5%, 95% confidence interval [CI]: 14.9-37.6). The cumulative incidence of VZV reactivation 1 and 2 years after HSCT was 6.26% (95% CI: 1.60-15.5) and 20.9% (95% CI: 10.3-34.0), respectively. While only one patient developed VZV reactivation during the administration of prophylactic acyclovir, the cumulative incidence of VZV reactivation increased to 24.2% (95% CI: 12.5-38.0) 1 year after the cessation of acyclovir.Low-dose acyclovir (15 mg/kg/day) could be effective for preventing VZV reactivation after HSCT in children because VZV reactivation seldom occurs during the administration of 15 mg/kg/day acyclovir.

Acute lymphoblastic leukemia (ALL) is the most common childhood cancer. As overall cure rates of childhood ALL have improved, reduction of overall treatment intensity while still ensuring excellent outcomes is imperative for low-risk patients. We report the outcomes of patients treated following the standard-risk protocol from the prospective Japan Association of Childhood Leukemia Study (JACLS) ALL-02 study, which was conducted between 2002 and 2008 for patients with newly diagnosed ALL aged 1-18 years. Of 1138 patients with B-cell precursor ALL, 388 (34.1%) were allocated to this protocol. Excellent outcomes were achieved despite the overall treatment intensity being lower than that of most contemporary protocols: 4 years event-free survival (EFS) was 92.3% and 4 years overall survival 98.2%. Patients with high hyperdiploidy (HHD) involving triple trisomy (trisomy of chromosomes 4, 10, and 17) or ETV6-RUNX1 had even better outcomes (4 years EFS 97.6% and 100%, respectively). Unique characteristics of this protocol include a selection of low-risk patients with a low initial WBC count and good early treatment response and reduction of cumulative doses of chemotherapeutic agents while maintaining dose density. In Japan, we are currently investigating the feasibility of this protocol while incorporating minimal residual disease into the patient stratification strategy.

Congenital leukemia is an extremely rare disorder that is diagnosed within the first 28 days of birth.1 Common clinical features of congenital leukemia include prominent hepatosplenomegaly and a hi...

Patients with multi-system (MS)-type langerhans cell histiocytosis (LCH) show poor outcomes, especially congenital MS LCH cases were shown in high mortality rate. We experienced a congenital case of MS LCH with high risk organs, who needed intensive respiratory support after birth. Even though intensive chemotherapy was discontinued, this patient's lung LCH lesions gradually became reduced and his respiratory condition recovered; therefore, we restarted and completed maintenance chemotherapy. The patient maintained complete remission for more than 4 years after the end of chemotherapy. Our case suggests that congenital MS LCH even with severe organ involvement can be treated successfully with chemotherapy.

Acute megakaryoblastic leukemia in children without Down syndrome (non-DS AMKL) is considered to be a poor prognostic subtype in acute myeloid leukemia. Recently, some chimeric fusion genes were found in pediatric non-DS AMKL; therefore, we attempted to detect chimeric fusion genes RBM15-MKL1, CBFA2T3-GLIS2, and NUP98-KDM5A from 10 pediatric non-DS AMKL diagnostic samples using polymerase chain reaction and Sanger sequencing methods. Two samples were positive for RBM15-MKL1, four had CBFA2T3-GLIS2, and only one case had NUP98-KDM5A. Both RBM15-MKL1-positive patients showed long-term remission after chemotherapy. The eight RBM15-MKL1-negative patients received hematopoietic stem cell transplantation (HSCT). In four CBFA2T3-GLIS2-positive patients, three had HSCT without complete remission and two of themdied. Additional treatment stratification depending on chimeric fusion genes and development of new therapeutic drugs are required for non-DS AMKL.

Acute lymphoblastic leukemia (ALL) is the most common malignancy in children. Although the cure rate of ALL has greatly improved, a considerable number of patients suffer from relapse of leukemia. Therefore, ALL remains the leading cause of death from cancer during childhood. To improve the cure rate of these patients, precisely detecting patients with high risk of relapse and incorporating new targeted therapies are urgently needed. This study investigated inexpensive, rapid, next-generation sequencing of more than 150 cancer-related genes for matched diagnostic, remission, and relapse samples of 17 patients (3 months to 15 years old) with relapsed ALL. In this analysis, we identified 16 single-nucleotide variants (SNVs) and insertion/deletion variants and 19 copy number variants (CNVs) at diagnosis and 28 SNVs and insertion/deletion variants and 22 CNVs at relapse. With these genetic alterations, we could detect several B cell precursor ALL patients with high-risk gene alterations who were not stratified into the highest-risk group (5/8, 62.5%). We also detected potentially actionable genetic variants in about half of the patients (8/17, 47.1%). Among them, we found that one patient harbored germline TP53 mutation as a secondary finding. This inexpensive, rapid method can be immediately applied as clinical sequencing and could lead to better management of these patients and potential improvement in the survival rate in childhood ALL.