PATH-08. PROGNOSTIC IMPLICATIONS FROM LONG-TERM SURVIVORS (LTS) OF GLIOBLASTOMA

Abstract

Glioblastoma (GBM) is the most aggressive primary brain malignancy with < 45% living a year beyond diagnosis which drops to 7% at five years. However, there have been reports of long-term survivors (LTS) living three to ten years beyond diagnosis. Few studies have reported on molecular factors in tumors from LTS cohorts. We identified GBM (IDH1/2 wildtype) patients living at least 3 years post diagnosis (N=25), including 16 with pre-treatment tumor tissue, from our Natural History Study. Available pre- or post-treatment tumors were analyzed with targeted panel sequencing and methylation analysis for classification, MGMT promoter status and copy number changes. Classical clinical prognostic features such as limited resection or older age did not preclude long-term survival as patients with tumor biopsy (n=1) or subtotal resection (n= 5) and patients > 60 were included in the LTS cohort. Furthermore, tumors with molecular features typically associated with poor prognosis were also in this GBM LTS group. MGMT promoter was unmethylated in 17% of tumors; EGFRvIII mutation in 13%, EGFR amplification in 33%, CDKN2A homozygous loss in 30% and complete chromosome 7 gain with 10 loss in 55%. Additionally, the methylation classifier found a higher-than-expected incidence of mesenchymal tumors (29%) and RTK II (57%). Tumors had a higher percent of TP53 mutations (44%) but lower pTERT (76%) compared to TCGA. These data suggest an individual patient’s prognosis cannot easily be predetermined based on classical clinical and molecular data. This underscores the need for further analyses to discover additional factors leading to their unexpected, prolonged survival and elucidate the role of factors typically associated with poor prognosis. Future work will include RNA-sequencing and germline whole genome sequencing to determine tumor specific gene expression and identify any possible genomic alterations that confer improved survival.