LGG-24. TEMPORAL GENOMIC HETEROGENEITY IN PEDIATRIC LOW-GRADE GLIOMAS

• Published in: Neuro-oncology (Charlottesville, Va.) Va.), 2018-06, Vol.20 (suppl_2), p.i109-i109
• Main Authors: Fuller, Christine, Schafer, Austin, Boue, Daniel, Osorio, Diana, Finlay, Jonathan, Rush, Sarah, Wright, Erin, Hoffman, Lindsey, Yanez-Escorza, Nancy, Reuss, Jamie, Hummel, Trent, Salloum, Ralph, Chow, Lionel M L, DeWire, Mariko, de Blank, Peter, Stevenson, Charles, Drissi, Rachid, Fouladi, Maryam
• Format: Article
• Language: English
• Subjects: Abstracts
• ISSN: 1522-8517; 1523-5866
• DOI: 10.1093/neuonc/noy059.365

Abstract INTRODUCTION Pediatric low-grade gliomas (pLGG) represent the most common brain tumors in children. Though malignant transformation is rare, these tumors pose a formidable therapeutic challenge due to anatomy-limiting surgical options and local recurrence. The temporal and therapy-driven genomic evolution in pLGG is largely unknown. METHODS To characterize the temporal genomic heterogeneity of pLGG, we performed fluorescence in situ hybridization, mutation-specific immunohistochemistry, and exome analyses on paired tumor samples from primary diagnostic and subsequent surgeries of 27 pLGG patients. RESULTS 59 tumor samples were available for review and included pilocytic / pilomyxoid astrocytoma (PA) (67%), low grade astrocytoma (19%), ganglioglioma (11%), and pleomorphic xanthoastrocytoma (3%). BRAF duplication/rearrangement was detected in 56% of tested samples, limited to PA in all but one patient (ganglioglioma). 58% of samples harbored CDKN2A deletion, which was demonstrable across various histologies. BRAF duplication/rearrangement was found consistently conserved across primary and subsequent surgical samples, whereas CDKN2A status changed in 60% of tested temporal pairs, with deletion acquisition the most frequent finding (40%) at second surgery. Likewise, BRAF V600E mutation in one PA was lost at second surgery. Although CDKN2A status changes were seen following surgery alone, the addition of chemo-and/or radiation therapy was associated with a higher rate of temporal CDKN2A deletion acquisition (50%, versus 33% with surgery alone). CONCLUSION Temporal genomic heterogeneity may be encountered in a significant proportion of pLGG, with some alterations potentially facilitated by therapy. Recurrence biopsy may provide improved guidance, particularly if targeted therapeutics are being considered.