Genomic Characterization of ETV6::RUNX1 ‐Positive Childhood B‐ALL in a Chinese Cohort: Novel Fusion Partners, Co‐Occurring Mutations, and Risk‐Stratifying Biomarkers

BACKGROUND: ETV6::RUNX1 is the most common genetic abnormality in pediatric B-cell acute lymphoblastic leukemia (ALL; ∼25%), yet the comprehensive genetic architecture and molecular predictors of intermediate-risk (IR) stratification remain incompletely characterized. METHODS: We performed whole-transcriptome sequencing (Illumina NovaSeq 6000, rRNA depletion, 41.70 Gb/sample) on bone marrow samples from 93 pediatric ETV6::RUNX1-positive B-ALL patients. Bioinformatics analysis included STAR alignment, MuTect2 variant calling, FusionCatcher fusion detection, and VEP annotation. The Jaccard index with permutation testing assessed mutation co-occurrence; logistic regression identified independent predictors of IR classification. RESULTS: Beyond ETV6::RUNX1, we identified 51 distinct fusion genes across the cohort, including the reciprocal RUNX1-ETV6 (73.1%), chr8::KLF1210 (38.7%), and KLF12-chr8 (34.4%). Somatic mutations in 249 genes were detected; the most frequent were KIAA1715 (17.2%), KRAS (11.8%), and NSD2 (10.8%). Network analysis revealed significant chromatin modifier co-occurrence (KIAA1715-KMT2C: J = 0.136, p = 0.015) and KRAS-NRAS mutual exclusivity (J = 0.000, p = 0.042). PTCH1 (OR = 3.50, 95% CI 0.21-58.49, p = 0.41) and GNB1 (OR = 6.5, 95% CI 1.2-34.8, p = 0.029) mutations independently predicted IR classification. chr8::KLF1210 fusion correlated with higher Day-19 MRD levels (p = 0.038). CONCLUSIONS: GNB1 mutation represents a novel independent predictor of IR stratification in ETV6::RUNX1-positive B-ALL. The chromatin modifier co-occurrence module and extensive fusion architecture reveal biological heterogeneity within this favorable-risk subtype, with potential implications for risk-adapted therapeutic strategies.