BI-19 * PSEUDOPROGRESSION IN OLIGODENDROGLIOMAS AND MIXED OLIGOASTROCYTOMAS IS ASSOCIATED WITH POOR PROGNOSIS

Abstract

INTRODUCTION: Pseudoprogression (PsP) is a radiologic phenomenon in which treatment results in disruption of the blood brain barrier resulting in areas of contrast enhancement that is indistinguishable from true tumor progression. In glioblastoma, PsP occurs more frequently in tumors with MGMT promoter methylation and is associated with a better prognosis. We investigated whether the two recurrent genetic alterations, 1p/19q codeletions and IDH1 R132H mutation, which have prognostic significance in oligodendrogliomas (OG) and oligoastrocytomas (OA), are associated with PsP. METHODS: Institutional review board approval was granted to query a pathologic database for grade II and III OG/OA and to perform IDH1 R132H immunohistochemistry on archival material. 139 patient cases were identified, in which serial imaging was performed, records were available for review, and the tumors were treated with fractionated radiotherapy. IDH1 R132H immunohistochemistry was performed on archival material from these cases when available and their charts were reviewed for clinical data. RESULTS: PsP occurred less frequently in OG/OAs with 1p/19q codeletions (8% of tumors) than tumors without 1p/19q codeletions (27% of tumors) with an odds ratio of 0.168 and 95% CI of 0.050-0.562 when adjusting for covariables by multivariate modeling. Within the cohort without 1p/19q codeletions, the development of PsP in OG/OA was independently associated with worse survival when compared to tumors without early contrast enhancement following treatment (p = 0.0059). Additionally, within this cohort without 1p/19q codeletions, 50% of the tumors with PsP were negative for IDH1 R132H mutation by immunohistochemistry, compared to 26% negativity among tumors without early contrast enhancement. CONCLUSIONS: In this study, we are the first to show that PsP occurs more frequently in OG/OA with a worse prognosis and that PsP may have an inverse association with 1p/19q codeletions and IDH1 R132H mutation.