Retroperitoneal Schwannoma with a Novel PRCC::TFE3 Fusion: Expanding the Spectrum of Schwannomas with a TFE3 Gene Rearrangement.

Although historically associated with the inactivation of the NF2 gene, a minority of schwannomas have recently been found to exhibit fusion transcripts, such as SH3PXD2A::HTRA1, NONO::TFE3, or VGLL fusions. Herein, we report a large retroperitoneal schwannoma exhibiting a PRCC::TFE3 fusion. Histologically, this tumor contained distinctive large epithelioid cells with granular cytoplasm, but also exhibited degenerative features often associated with schwannoma, such as perivascular hyalinization and hemosiderin deposition. The cells were positive for SOX10, showed robust TRIM63 expression, and were focally positive for HMB45. Methylation profiling confirmed that the tumor was of Schwann cell differentiation. Following complete surgical resection, the patient has experienced no recurrence to date. As MiT family translocation-associated renal cell carcinoma and alveolar soft part sarcoma can also exhibit a PRCC::TFE3 fusion, awareness of this rare schwannoma subtype is vital in ensuring it is not mistaken for a more aggressive neoplasm.