PATH-52. ANAPLASTIC PILOMYXOID ASTROCYTOMA HARBORING BRAF FUSION, PTEN AND TERT MUTATIONS

Abstract Pilomyxoid astrocytomas (PMA) are focal neoplasms that are often cured with total resection. We present a case of a progressive PMA with histologic and molecular features suggestive of malignant transformation. A 13-year old boy presented with headaches, diplopia, and seizures. He had previously been followed for 7 years by serial imaging for a cystic/solid enhancing mass in the right temporal lobe without biopsy that had remained stable up to 6 months prior to his current illness. MRI of brain demonstrated significant progression of the solid component with extension into the subependymal portions of the lateral ventricles, leptomeningeal spread in brain and spine, and hydrocephalus. Patient underwent a partial resection of tumor and VP shunt placement. Pathology demonstrated a prominent myxoid matrix with angiocentric arrangement of monomorphous bipolar cells. PHH3 and Ki-67 stains confirmed multiple mitoses and elevated proliferation rate. Next Generation sequencing of tumor confirmed the presence of a KIAA1549-BRAF duplication/fusion, CDKN2A deletion, along with PTEN and TERT promoter mutations without BRAF V600E or ATRX mutations. The histology and molecular features was suggestive of a pilomyxoid astrocytoma (PMA) with anaplastic transformation. Patient is currently receiving carboplatin + vincristine plus a MEK inhibitor (TrametinibTM, Novartis Corporation, Cambridge, MA) for tumor control. We believe that the tumor was initiated by the oncogenic BRAF fusion and the dramatic progression and spread of disease after a long period of stability was probably related to recent acquisition of additional deleterious mutations that have been previously reported in anaplastic pilocytic astrocytoma.