PATH-38. INTRACRANIAL SARCOMA WITH DICER1 MUTATION IN A PATIENT WITH NEUROFIBROMATOSIS TYPE 1

Abstract A 16-year-old male with neurofibromatosis type 1 (NF1) and a history of low-grade gliomas presented for resection of a progressively enlarging, known low-grade glioma. On follow-up imaging for surgical planning of the low-grade glioma, a new area of concern was detected of a leptomeningeal-based lesion over the left frontal lobe. A biopsy of the frontal lobe lesion subsequently showed a primary intracranial sarcoma with DICER1 mutations, DICER1 p.Q1552 and p.D1709G. An important histology finding was that of prominent eosinophilic cytoplasmic globules, which are associated with intracranial sarcomas with DICER1 mutations. Additional molecular findings of this tumor included NF1 p.K1986fs and TP53 p.G279E mutations in the setting of this patient’s known history of NF1. A DICER mutation was not detected in the concurrent low-grade glioma at the time of his intracranial sarcoma diagnosis, thus thought not to be a germline-derived mutation. He went on to have a surgical resection with subsequent photon radiation therapy followed by consolidation chemotherapy. A Ewing sarcoma based regimen as per COG protocol AEWS1031 was selected for his therapy consisting of vincristine, doxorubicin, cyclophosphamide alternating with ifosfamide, etoposide (VDC-IE). This was chosen based on prior cases showing response to anthracycline-based regimens. This patient has overall shown improvement without signs of progression now 7 months out from his initial diagnosis. This case highlights the importance of recognizing the association of patients with NF1 being at an increased risk for the development of intracranial sarcomas with DICER1 mutations and correlation with histologic findings of eosinophilic cytoplasmic globules. It also points to the need for reporting these rare cases for optimization of therapy selection to provide a more standardized and evidence-based approach in the care for these patients.