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Objective: The central nervous system (CNS) is a frequent site of relapse in childhood acute lymphoblastic leukemia (ALL). This study aims to investigate the utility of cerebrospinal fluid (CSF) flow cytometry in detecting CNS infiltration and relapse. Methods: Flow cytometry was used to detect CSF leukemia cells, and patients were categorized into the CSF Flow+ and CSF Flow− groups. The primary outcome was the cumulative incidence of relapse (CIR) in the CSF Flow+ and CSF Flow− groups. Results: A total of 1301 patients were enrolled, 159 patients (12.2%) showed positive CSF flow cytometry results. The CNS Flow+ patients exhibited significantly higher rates of any CNS relapse (22.5% vs. 0.2%, p < 0.01) and isolated CNS relapse (10.7% vs. 0%, p < 0.01) compared to CNS Flow− patients. Cox regression analysis revealed that risk factors for isolated CNS relapse included a positive result of D46 minimal residual disease (MRD) and CSF Flow+ at a non‐initial diagnosis. For any CNS relapse, the significant risk factors were CSF Flow+ at the initial diagnosis and CSF Flow+ at a non‐initial diagnosis. Conclusions: CSF flow cytometry may have clinical utility in detecting CNS infiltration among pediatric ALL patients. It could contribute to more effective risk stratification and treatment adjustments and potentially reduce the risk of CNS relapse. [ABSTRACT FROM AUTHOR]

Background: PDGFRB fusions in acute lymphoblastic leukemia (ALL) is rare. The authors identified 28 pediatric PDGFRB‐positive ALL. They analyzed the features, outcomes, and prognostic factors of this disease. Methods: This multicenter, retrospective study included 6457 pediatric patients with newly diagnosed PDGFRB fusion ALL according to the CCCG‐ALL‐2015 and CCCG‐ALL‐2020 protocols from April 2015 to April 2022 in 20 hospitals in China. Of these patients, 3451 were screened for PDGFRB fusions. Results: Pediatric PDGFRB‐positive ALL accounted for only 0.8% of the 3451 cases tested for PDGFRB. These patients included 21 males and seven females and 24 B‐ALL and 4 T‐ALL; the median age was 10 years; and the median leukocyte count was 29.8 × 109/L at baseline. Only one patient had eosinophilia. Three patients had an IKZF1 deletion, three had chromosome 5q31‐33 abnormalities, and one suffered from a complex karyotype. The 3‐year event‐free survival (EFS), overall survival (OS), and cumulative incidence of relapse (CIR) were 33.1%, 65.5%, and 32.1%, respectively, with a median follow‐up of 25.5 months. Twenty patients were treated with chemotherapy plus tyrosine‐kinase inhibitors (TKIs) and eight were treated without TKI. Complete remission (CR) rates of them were 90.0% and 63.6%, respectively, but no differences in EFS, OS, or CIR. Univariate analyses showed patients with IKZF1 deletion or measurable residual disease (MRD) ≥0.01% after induction had inferior outcomes (p <.05). Conclusions: Pediatric PDGFRB‐positive ALL has a poor outcome associated with high‐risk features. Chemotherapy plus TKIs can improve the CR rate, providing an opportunity for lower MRD levels and transplantation. MRD ≥0.01% was a powerful adverse prognostic factor, and stratified treatment based on MRD may improve survival for these patients. Plain Language Summary: Pediatric acute lymphoblastic leukemia patients with PDGFRB fusions are associated with high‐risk clinical features such as older age, high white blood cell count at diagnosis, high measurable residual disease after induction therapy, and increased risk of leukemia relapse.Chemotherapy plus tyrosine‐kinase inhibitors can improve the complete remission rate and provide an opportunity for lower measurable residual disease (MRD) levels and transplantation for pediatric PDGFRB‐positive acute lymphoblastic leukemia (ALL) patients.The MRD level was also a powerful prognostic factor for pediatric PDGFRB‐positive ALL patients. Pediatric acute lymphoblastic leukemia (ALL) patients with PDGFRB fusions are associated with high‐risk clinical features. Chemotherapy plus tyrosine‐kinase inhibitors can improve the complete remission rate and provide an opportunity for lower measurable residual disease (MRD) levels and transplantation for pediatric PDGFRB‐positive ALL patients. The MRD level was also a powerful prognostic factor for pediatric PDGFRB‐positive ALL patients. [ABSTRACT FROM AUTHOR]