Pseudoglandular Schwannoma With FUS::KLF17 Fusion: Broadening the Spectrum of FUS-Associated Tumors

We present a case of a 51-year-old male with a pseudoglandular cellular schwannoma arising from the brachial plexus, which contains the expected molecular aberrations for a schwannoma (chromosome 22q loss encompassing the NF2 and LZTR1 genes) as well as a FUS::KLF17 rearrangement. Pseudoglandular schwannomas are rare morphologic variants of schwannomas that contain gland-like spaces lined by S100-positive, cytokeratin-negative pseudocolumnar Schwann cells. Fusions involving FUS and EWSR are commonly found in myoepithelial tumors of bone and soft tissue. While the spectrum of tumors with fusions involving FUS and EWSR is relatively broad, no cases, to our knowledge, have been reported of schwannomas, let alone the morphologically distinct pseudoglandular schwannoma, containing a FUS rearrangement. This case thus expands the spectrum of FUS rearranged tumors, highlighting the need for documentation of similar cases to understand the clinical significance of this combination.