PATH-43. HISTOLOGY OF RADIATION-INDUCED PSEUDOPROGRESSION WITH MULTIPLE FOCI IN TREATED GLIOBLASTOMA

Abstract Radiation induced pseudoprogression (PsP) of brain tumors is defined radiologically as new or enlarging areas non-tumor magnetic resonance imaging (MRI) contrast enhancement developing within the initial 3-6 months after completing radiation. Distinguishing PsP from genuine tumor progression utmost importance in deciding clinical course a patient. Although it typically diagnosed radiologically, obtaining tissue histopathology can clarify diagnostic uncertainty. However, there no consensus on defining pathologically. We present case 38-year-old man with glioblastoma, IDH-wild type, CNS WHO Grade 4 (MGMT promoter methylated) steroid-refractory PsP, and correlate both radiologic pathologic features. After treatment gross total resection radiation concurrent temozolomide, he developed contrast-enhancing, mass-neutral enhancing lesion consistent which did not resolve despite cycles temozolomide prolonged steroid treatment. The was resected, pathological examination demonstrated non-pseudopallisading necrosis, numerous macrophages, astrocytosis, hyalinization blood vessels, low mitotic activity parenchyma residual infiltrative glioma. These features were radiation-treatment effect supported diagnosis PsP. Over time, varying definitions for include percentage threshold necrosis per sample. authors recognize potential sampling bias. Therefore, we recommend including treatment-related effects coupled absence proliferation results. fibrinoid eosinophilic coagulation necrosis. From therapeutic standpoint, important to comment presence glioma cell proliferation. This highlights unique paring focal correlative sections MRI has been previously presented.