Delineation of features, responses, outcomes, and prognostic factors in pediatric PDGFRB-positive acute lymphoblastic leukemia patients: A retrospective multicenter study.
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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.