BIOM-18. TUMOR LOCATION IS ASSOCIATED WITH CDKN2A STATUS IN IDH-MUTANT ASTROCYTOMAS

Abstract

Abstract BACKGROUND Astrocytomas with isocitrate dehydrogenase (IDH) mutations have a better prognosis and response to therapy than matching tumors without IDH mutations. IDH-mutant tumors of any grade or histology that carry homozygous deletions in cyclin-dependent kinase inhibitor (CDKN2A) have a worse prognosis compared to tumors with intact CDKN2A. Within a retrospective cohort of IDH-mutant astrocytomas with known CDKN2A status, we examined whether there was any correlation of CDKN2A status with anatomic location. METHODS Astrocytomas of any grade carrying IDH mutations with further molecular sequencing that included CDKN2A status were identified from a tissue database, as well as a clinical cohort of patients seen at the neuro-oncology clinic who had genomic analysis by clinical request. Imaging was reviewed for tumor location. Fisher’s exact test was used to analyze differences between groups. RESULTS Six of 35 IDH-mutant astrocytomas (17%) had CDKN2A deletions. None of the six patients with CDKN2A mutant tumors had contact with the insula, whereas 16 of 29 tumors (55%) with intact CDKN2A contacted the insula (p=0.02). The majority of tumors in both groups were located completely or partially in the frontal lobe, as is common in IDH-mutant astrocytomas, and all CDKN2A deleted tumors were in the frontal lobe. DISCUSSION Astrocytomas with IDH mutations that also carry CDKN2A deletions have been shown to have a worse prognosis than similar grade tumors with intact CDKN2A status. This has important prognostic implications, but CDKN2A testing is not standard currently or used to stratify patients in clinical trials. Our sample size is small, but if confirmed in a larger cohort could help guide efficient testing for CDKN2A status and improve prognostication.