PATH-31. COMPLETE TUMOR DISAPPEARANCE ON BRAIN MRI AFTER STANDARD CHEMORADIATION THERAPY FOR A MOLECULAR GLIOBLASTOMA

Abstract INTRODUCTION Glioblastoma (GBM) is the most aggressive brain tumor. The WHO CNS5 classification has newly incorporated three molecular criteria in diagnosing molecular GBM, including a concurrent gain of chromosome 7 and loss of chromosome 10 (+7/-10), TERT promoter mutation, or EGFR amplification. Despite new classification, the Stupp protocol remains the standard of care for all GBMs. However, it is unclear if the treatment response of the molecular GBM with low grade features is the same as the limited response of the traditional histopathological GBM. CASE REPORT A 74-year-old male presented in August of 2023 with new onset left-sided facial numbness. The numbness resolved spontaneously that day. Brain MRI was notable for a diffuse left frontal T2/Flair hyperintense lesion extending across the corpus callosum into the right frontal lobe without definite enhancement. Brain biopsy from 8 sites of the tumor demonstrated a subset of areas with mild hyper-cellularity, suggesting a low-density infiltrating glioma. However, TERT promoter mutation (-124C>T), was detected along with wild-type IDH1, supporting molecular GBM. Studies also found unmethylated MGMT gene promotor. Brain MRIs after 3 and 6 months showed no tumor progression. The patient has remained asymptomatic apart from baseline mild forgetfulness. He was started on the 6-week standard concomitant temozolomide and radiation therapy. Follow-up brain MRI after the above treatment showed complete imaging resolution of the tumor. DISCUSSION It is very rare for complete imaging resolution of GBM on brain MRI after standard 6-week chemoradiation therapy. Our case suggests that molecular GBM with low-grade features on imagine and pathology might have a better response to the standard treatment than traditional histopathological GBM even though the molecular GBM patient has unfavorable prognostic factors such as unmethylated MGMT and older age (>70 years old). Our experience emphasizes the heterogenous response of molecular GBM to the current standard treatment.