Primary central nervous system histiocytic sarcoma with somatic NF2 mutation: Case report and review of literature.

Primary histiocytic sarcoma of the central nervous system is a rare lymphohematopoietic tumor originating from histiocytes. Here we report such a case with somatic NF2 mutation. Based on imaging studies, a 24-year-old woman presented with a homogeneously enhancing lesion in the right parietal lobe region and without other organ involvement. Histological analysis showed that the pleomorphic tumor cells were loosely arranged, and the neoplastic cells are characterized by abundant eosinophilic cytoplasm, highly atypical nuclei, and prominent nucleoli. The lesional cells were immunoreactive with antibodies against -CD68KP1, CD163 focally, lysozyme, and BRAF V600E. NGS-based genetic profiling revealed a pathogenic somatic NF2 (p.R196*) mutation. Additionally, BRAF (p.V600E), PDGFRA (p.V561D), BRCA1 (p.H437Q, VUS), and BRCA2 (p.E2343A, VUS) mutations were detected. However, the tumor did not respond to apatinib and anlotinib treatment, and the patient died 10 months after the initial diagnosis.