Abstract A023-PR006: CBL mutations in pediatric solid and CNS tumours are a marker of receptor tyrosine kinase activation and a potential therapeutic target

Abstract Molecularly targeted therapies, selected using precision medicine approaches like the Zero Childhood Cancer Program (ZERO), improve outcomes for childhood cancer patients. Mutations in the E3 ubiquitin ligase, CBL, represent one such molecular target in acute myeloid leukaemia, where mutation mediates activation of the Receptor Tyrosine Kinase (RTK), FLT3, and sensitivity to FLT3-targeted Tyrosine Kinase Inhibitors (TKIs). We have identified novel CBL mutations in pediatric CNS and solid tumours, raising the possibility of targeting RTKs activated by CBL mutations in other tumour types. We analyzed whole genome and RNA sequencing data from the ZERO cohort and identified 34 somatic and 2 germline CBL variants in 31 individual patients. The majority of CBL variants (72% [26/36], including 24 somatic and 2 germline), clustered around key functional domains, the linker region and RING finger domain, and were predicted to be pathogenic based on their location. Somatic CBL variants were identified in 6 leukemia samples (27% [6/22]), including 5 AML cases. The remaining CBL mutated samples were from non-hematological malignancies (73% [16/22]), including 1 neuroblastoma, 1 germ cell tumour and 14 CNS tumour samples. The neuroblastoma and germ cell tumour cases both harbored the established pathogenic CBL exon8/9 genomic deletion (CBL ex8/9Δ), while CNS tumours expressed either CBL missense (8 samples) or splice (6 samples) mutations that were either novel, variants of uncertain significance and/or not previously identified in this tumour type. CBL mutated CNS tumours were molecularly diverse and commonly did not classify into pre-defined DNA methylation-based subtypes (5/13 cases, where methylation analysis was performed). We show that overexpression of the CBL ex8/9Δ in neuroblastoma cell lines enhanced cell proliferation and blocked CBL mediated degradation of RTKs, resulting in maintained RTK signaling. Interestingly, high-throughput screening of the patient sample in which this variant was identified, revealed sensitivity to the multi-TKI pazopanib. We also demonstrate that novel CBL variants, identified in pediatric CNS tumours, can cooperate with RTK overexpression to drive transformation. Thus, we show that CBL mutations are a marker of RTK activation in non-hematological tumors. This finding will extend the potential benefit of TKIs, which have proven efficacy in paediatric cancer, to more patients. Citation Format: Lauren M Brown, Chelsea Mayoh, Katherine A Camper, Pablo Acera Mateos, Wenyan Li, James Bradley, Teresa Sadras, Robert Salomon, Marie Wong, Mark J Cowley, Antoine de Weck, Loretta MS Lau, Neevika Manoharan, Paul G Ekert. CBL mutations in pediatric solid and CNS tumours are a marker of receptor tyrosine kinase activation and a potential therapeutic target [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Discovery and Innovation in Pediatric Cancer— From Biology to Breakthrough Therapies; 2025 Sep 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl_2):Abstract nr A023-PR006.