Abstract
PURPOSE: Tumors previously diagnosed as solitary fibrous tumors (SFT) and hemangiopericytomas (HPC) are characterized by the NAB2-STAT6 fusion gene, leading to nuclear STAT6 expression, and are now considered part of one SFT/HPC tumor entity by the 2016 World Health Organization Classification of Tumors of the Central Nervous System. We present the first primary choroidal SFT/HPC with the diagnosis confirmed by STAT6 expression. PROCEDURES: A 51-year-old man underwent enucleation for a choroidal mass, which revealed a spindle cell neoplasm involving the optic nerve, without extrascleral extension. Immunohistochemical stains for S-100, melan-A, tyrosinase, and HMB45 were all negative; however, detection of monosomy 3 by FISH favored a choroidal spindle cell melanoma. Four years later, he presented with hepatic metastases of a spindle cell tumor, and a year later with an epithelioid malignancy involving the calvarium. RESULTS: The calvarial tumor showed nuclear STAT6 immunoreactivity, supporting the diagnosis of SFT/HPC. Retrospectively, the choroidal and hepatic masses were also found to demonstrate nuclear STAT6 expression, supporting the diagnosis of a primary choroidal SFT/HPC with metachronous metastases to the liver and calvarium. CONCLUSIONS: This case highlights the significance of considering SFT/HPC in the diagnosis of intraocular spindle cell tumors and the importance of STAT6 immunohistochemistry in the evaluation of such tumors.