Uterine Tumor Resembling Ovarian Sex Cord Tumor With GREB1::NCOA2 Fusion and Neuroendocrine Marker Expression: A Case Report and Literature Review.

The uterine tumor resembling ovarian sex cord tumor (UTROSCT) is a rare mesenchymal tumor of the uterus. Morphological patterns can show sheets, cords, and trabeculae that are similar to those seen in ovarian sex cord-stromal tumors. Immunohistochemically, they exhibit a polyphenotypic variable pattern, including epithelial, myoid, and sex cord lineage as well as hormone receptors. We report a female patient with a UTROSCT harboring a GREB1::NCOA2 fusion that demonstrated a diffuse, strong positivity with chromogranin, synaptophysin, and CD56. INSM1 was performed to rule out true neuroendocrine differentiation. While neuroendocrine marker expression is rare in UTROSCT, this report adds to the limited literature describing this unusual immunoprofile, particularly in the context of GREB1 rearrangements. This study remains important to highlight the inclusion of this type of immunohistochemical staining in the spectrum of features UTROSCT can represent. Recent systematic review evidence suggests that GREB1-rearranged UTROSCTs may represent a biologically and clinically distinct subset from ESR1-rearranged tumors, with differences in clinicopathological features and molecular characteristics.