[Two Cases of Primary Intracranial Solitary Fibrous Tumor:Genetic Examination of <i>NAB2-STAT6</i> Fusion and Its Association with Hemangiopericytoma].

Using whole exome and transcriptome sequencing, NAB2-STAT6 gene fusions have recently been identified in patients with solitary fibrous tumors (SFT). We report two cases of SFT in which NAB2-STAT6 fusions were identified. The patients were a 32-year-old man with a parasagittal tumor involving the superior sagittal sinus, and a 40-year-old man with a cerebellar convexity tumor partially involving the transverse sinus. Their tumors were gross totally resected and diagnosed to be SFT according to the following pathological findings:the tumors were composed of spindle cells with a patternless architecture, with prominent stromal collagen and staghorn vessels. An immunohistochemical study yielded positive results for CD34, CD99, and Bcl-2 and negative results for EMA, GFAP, and S100. The MIB-1 indexes were 13 and 7%, respectively. NAB2-STAT6 fusions were detected in both cases with a common fusion variant, NAB2ex6-STAT6ex16/17. We also identified NAB2-STAT6 fusions in two hemangiopericytomas diagnosed in the past with a common variant of NAB2ex6-STAT6ex16/17. These findings suggest that solitary fibrous tumor and hemangiopericytoma may be diagnosed based on the presence of NAB2-STAT6 fusion, and not classified separately because of the same genetic background.