Spinal solitary fibrous tumor of the neck: Next-generation sequencing-based analysis of genomic aberrations

A solitary fibrous tumor (SFT) is a rare neoplasm with recurrent NAB2–STAT6 gene fusion. An SFT may develop almost anywhere throughout the body, including the head and neck region, and is characterized by a broad spectrum of malignancy. Here we present a case involving a 57-year-old male with a dumbbell-shaped SFT in the cervical spine that mimicked schwannoma. Repeated fine-needle aspiration cytology failed to establish a definitive diagnosis. Given that the tumor size increased significantly over a 10-month period, open biopsy was then performed. Though the biopsy result was inconclusive, a nonepithelial tumor, including sclerosing epithelioid fibrosarcoma or ossifying fibromyxoid tumor, was suspected. The tumor was then completely removed together with adjacent parts of C2 and C3 vertebrae and left vertebral artery via combined anterior and posterior approaches. Histologically, the tumor consisted of round cells with prominent stromal hyalinization and was immunohistochemically positive for STAT6, CD34, and cytokeratin. Finally, Todai OncoPanel, a next-generation sequencing-based molecular profiling system using formalin-fixed paraffin-embedded samples, demonstrated fusion transcript in which NAB2 exon 6 was fused to STAT6 exon 16 supporting the diagnosis of SFT, while whole-exome sequencing analysis detected no somatic mutations which were known to be oncogenic.