P14.19.B PRIMARY HISTIOCYTIC SARCOMA OF THE CENTRAL NERVOUS SYSTEM: REPORT OF TWO CASES, INCLUDING A CASE WITH PROMINENT INTRAVENTRICULAR DISSEMINATION

Abstract BACKGROUND Primary Central Nervous System histiocytic sarcoma is rare aggressive malignant neoplasm with less that 50 cases reported in the literature. They usually harbor variable genetic alteration including MAPK and PI3K pathways as well as tumor suppressor genes TP53 and CDKN2A/B, among others. Herein, two additional two cases of Primary CNS histiocytic sarcoma are reported. MATERIAL AND METHODS N/A. RESULTS Case 1: 78-year-old man with past medical history significant for renal cell carcinoma (25 years ago), and chronic kidney disease, presented with gait instability and multiple falls. Magnetic resonance imaging (MRI) and Positron Emission Tomography-Computed Tomography (PET/CT) scan revealed prominent intraventricular dissemination with multiple enhancing masses along the ventricular system and periventricular areas that were enlarging over time. In addition, there were multiple intramedullary, central canal and pial surface lesions in the cervical spine. Also left adreanal adenoma was seen and small indeterminate lesions in the liver and left kidney. Overall findings were suspicious for primary CNS malignancy. Biopsy revealed histiocytic sarcoma. Given the advanced stage of disease the patient opted for palliative therapy and eventually passed away 14 days after the diagnosis. Case 2: 56-year-old woman with medical history of breast carcinoma (2021) and hypertension presented with one year history of bilateral feet and calf paresthesia, followed by repeated falls and eventually becoming wheelchair-bound. She also developed hearing impairment, dysarthria, dysphagia and abnormal extraocular movements. Multiple brain MRIs revealed extensive extra-axial and leptomeningeal enhancement involving bilateral cavernous sinuses, optic chiasm and tracts, prepontine cistern and adjacent temporal regions. Nodular enhancement along cranial nerves and brainstem was also noted. Excisional biopsy revealed histiocytic sarcoma. Patient clinically deteriorated rapidly and passed away 10 days after the diagnosis. Pathology: Both cases revealed high-grade malignancy composed of sheets of large cells with ample cytoplasm. Significant nuclear pleomorphism and multinucleation was seen. Background chronic inflammation was present. Large neoplastic cell were positive for histiocytic markers, including CD68, CD163, CD4, PU.1 and S100, while all other lymphoma, epithelial, melanocytic and sarcoma markers were negative. MayoComplete Histiocytic Neoplasm panel was negative for all 8 mutations tested. CONCLUSION Primary CNS histiocytic sarcoma is a very rare entity. These two cases support the previously reported aggressive clinical course of primary CNS histiocytic sarcoma. Histiocytic sarcoma can involved any area of central nervous system, but prominent intraventricular dissemination as seen in case 1 has been previously reported in only case.