PATH-55. "UNRAVELING THE COMPLEXITIES OF RECURRENT PLEOMORPHIC XANTHOASTROCYTOMA: INSIGHTS FROM ABERRANT IMMUNOHISTOCHEMISTRY AND BRAF V600E MUTATION."

Abstract

Abstract INTRODUCTION Pleomorphic xanthoastrocytoma (PXA) is a rare brain tumor that accounts for less than 0.3% of primary central nervous system (CNS) tumors, with an annual incidence of less than 0.7 cases per 100,000 population. PXAs typically express glial fibrillary acidic protein (GFAP), and S100 is often diffusely positive in these tumors. Objetive: To present a long-term multi-recurrence of PXA spanning 12 years which exhibits unusual histological features and an aberrant immunophenotype profile. Patient and methods: We reevaluted the primary tumor, performed a wide panel of immunohistochemistry ( Benchmark Gx Roche) and add molecular testing of BRAFp.V600E mutation and CDKN2 deletion. RESULTS The tumor present fibrillar and epitheliod features in the first recurrence and rhabdoid morphology in the subsequent two resections. All of them were characterized by the absence of GFAP and S100 expression with focal myogenin positivity. This variation in immunohistochemistry adds to the diagnostic challenge in identifying the tumor correctly.The patient's clinical history and the molecular results played a crucial role in defining the diagnosis and guiding treatment decisions. After complete surgical resection the patient received anti-BRAF treatment and has shown an excellent clinical response thus far. CONCLUSIONS This case highlights the extreme pleomorphism of PXA, as evidenced by the unusual histological features and aberrant immunophenotype observed. It emphasizes the diagnostic challenge presented when morphological and immunohistochemical characteristics deviate from the usual pattern. Molecular biology techniques, including genetic testing, are crucial in such cases to aid in accurate diagnosis, guide treatment decisions, and improve patient outcomes.