MOLECULAR PROFILING REVEALS NOVEL GENE FUSIONS AND GENETIC MARKERS FOR REFINED PATIENT STRATIFICATION IN PEDIATRIC ACUTE LYMPHOBLASTIC LEUKEMIA.

Risk-adapted treatment protocols conferred remarkable improvement in the survival rates of pediatric acute lymphoblastic leukemia/lymphoma (ALL/LBL). Nevertheless, clinical management is still challenging in certain molecular subgroups and in the presence of alterations associated with an increased rate of relapse. In this study, disease-relevant genomic and transcriptomic profiles were established in a prospective, multicenter, real-world cohort involving 192 children diagnosed with ALL/LBL. Gene fusions were detected in 34.9% of B-ALL and 46.4% of T-ALL patients, with novel chimeric genes involving JAK2, KMT2A, PAX5, RUNX1 and NOTCH1, and with KMT2A-rearranged patients displaying the worst 3-year event-free survival (p=0.019). Non-synonymous mutations were uncovered in 74.9% of the analyzed patients, and a pairwise scrutiny of genetic lesions revealed recurrent clonal selection mechanisms commonly converging on the same pathway (e.g. Ras, JAK/STAT and Notch) in individual patients. Investigation of matched diagnostic and relapse samples unraveled complex subclonal variegation, and mutations affecting the NT5C2, TP53, CDKN2A, and PIK3R1 genes, emerging at the time of relapse. TP53 and CREBBP mutations, even as subclonal aberrations, were associated with shorter 3-year event-free survival among all patients with B-ALL (TP53 mutant vs wild-type: p=0.008, CREBBP mutant vs wild-type: p=0.010); and notably, B-ALL patients showing no measurable residual disease on day 33 could be further stratified based on TP53 mutational status (p<0.001). Our in-depth molecular characterization performed across all risk groups identified novel opportunities for molecularly targeted therapy in 55.9% of high-risk and in 31.6% of standard/intermediate-risk patients.