Glial Fibrillary Acidic Protein (GFAP)-Expressing Metastatic Carcinoma to the Brain: A Case Report

Presented here is a case of a 69-year-old man with undefined lung nodules who was found to have enhancing masses in the right superior frontal and right precentral gyri. The tumor displayed pathologic features initially suggestive of glioblastoma, including diffuse but atypical glial fibrillary acidic protein (GFAP) expression, positive but weak oligodendrocyte transcription factor 2 (Olig2) staining, high mitotic activity, and pseudopalisading necrosis. However, next-generation sequencing revealed no glioblastoma-associated genetic alterations but did reveal a mutation in DICER1, a gene encoding an RNA endoribonuclease implicated in malignant lung tumors. Further investigation via tumor methylation profiling revealed a strong match with lung adenocarcinoma. This case offers a rare presentation of GFAP-positive lung adenocarcinoma metastasis to the brain and validates the combined histological, immunohistochemical, and molecular approach to brain tumor diagnosis.