LGG-38. PROTEOGENOMICS REVEALS THREE DISTINCT BIOLOGICAL PILOCYTIC ASTROCYTOMA SUBGROUPS

Pilocytic astrocytoma (PA) is the most common pediatric brain tumor. Aberrant MAPK signaling, typically mediated by BRAF alterations, drives PA formation. While five-year overall survival rates exceed 95%, incompletely resected tumors recur frequently despite treatment. Therefore, we used proteogenomics to discern the biological heterogeneity of PA to improve classification of this tumor entity and identify novel therapeutic targets. Our proteogenomics approach utilizes RNA sequencing and LC/MS-based proteomic profiling and Similarity Fusion Network (SNF) analysis reveals the biological heterogeneity of PA. Integrative genomics dissects aberrant pathway activation in biological subgroups. Lastly, we utilize a drug screening pipeline to evaluate selective therapeutic activity of conventional anti-cancer and phase III/IV clinical trial drugs in PA culture models. PAs segregate into three groups with distinct clinical and molecular features. Age and tumor location are significantly associated with the SNF groups. BRAF fusions were predominantly observed in Groups 1 and 2, while Group 3 PA largely harbored other alterations leading to MAPK activation. Pathway enrichment analyses reveals genesets involved in primary ciliogenesis in Group 3, while immune response signatures, many SYK-related, are associated with Group 1. Confirming this analysis, the SYK inhibitor R788 was specifically active in Group 1, and less active in other brain tumors models (n=27). In summary, our proteogenomic approach reveals important biological heterogeneity with novel therapeutic targets emerging in PA. These biological insights may improve biological classification and reveal novel therapeutic targets specifically useful for non-resectable tumors with high risk of progressive disease.