PATH-14. MOLECULAR ANALYSIS OF ASTROCYTOMAS WITH A DOMINANT PILOMYXOID MORPHOLOGY

Abstract Pilomyxoid astrocytomas (PMAs) are tumors of infancy occurring in the hypothalamic chiasmatic region, with somewhat worse prognosis than pilocytic (PAs). We report molecular findings PAs a dominant pilomyxoid histomorphology across various age groups and CNS locations. Foundation Medicine comprehensive genomic profiling (CGP) (FoundationOne, FoundationOneCDx, FoundationOneHeme) were performed during routine clinical care. A retrospective cohort analysis was done to evaluate characteristics PMAs. 57 PMAs identified, which 6 occurred patients < 12 months old (10.5%); 14 1-3 year (24.6%); 15 4-10 y.o. (26.3%); 11-20 (21.1%), 10 young adults 21-39 (17.5%). 30/57 (52.6%) female 27/57 (47.4%) male. 55 brain 2 spinal cord. Tumors categorized by notable rearrangements point mutations. The common fusion, KIAA1549:BRAF, detected 23/57 samples (40.4%). BRAF fusions other gene partners (BRAF, TAX1BP1) 2, V600E mutations 4 patients. An additional had FGFR1 (FGFR1, TACC1) FGFR Other alterations included 3 NF1 mutations, NTRK family receptor tyrosine kinase fusions, RAF (ATRX, ALK) alterations, 1 VUS. Tumor Mutational Burden under mut/Mb for all In this PMAs, MAPK pathway genetic drivers, similar PAs. also observed frequent not involving BRAF, including members that have FDA approved targeted inhibitors. While these likely cause activation, non-BRAF variants less Our contributes growing evidence harbor distinct alteration profile, is becoming increasingly important context evolving therapeutics landscape.