MEIS1::NCOA2 Rearranged Spindle Cell Neoplasm of Vulva With Unusual Low-Grade Morphology.

MEIS1::NCOA2 is a recurrent gene fusion that has been predominantly identified in primitive sarcomas arising within the genitourinary and gynecological tracts. Since its initial description in 2018, an increasing number of cases have been reported, further defining the clinicopathological spectrum of this entity. We report a case of an MEIS1::NCOA2-rearranged low-grade myxoid spindle cell neoplasm arising in the vulva of a 31-year-old female, presenting as a polypoid mass. Histologically, the lesion was composed predominantly of hypocellular spindle-cell areas, with focal hypercellular and focal myxoid regions. Immunohistochemistry was nonspecific, demonstrating weak, variable expression of estrogen receptor (ER) and focal positivity for desmin, WT1, smooth muscle actin, and h-caldesmon. RNA-based next-generation sequencing identified a MEIS1::NCOA2 fusion transcript, which was subsequently confirmed by fluorescence in situ hybridization (FISH), demonstrating NCOA2 rearrangement. This case demonstrates remarkably bland, low-grade cytological features and appears to represent the least cytologically atypical example of this neoplasm described to date. As such, it further extends the known morphological spectrum and contributes to our evolving understanding of this entity. Given the deceptively benign histological appearance and the absence of overt sarcomatous features, we favor the designation of "MEIS1::NCOA2-rearranged low-grade myxoid spindle cell neoplasm" rather than sarcoma.