Uterine tumor resembling ovarian sex cord tumor (UTROSCT) is a rare, typically benign uterine tumor occurring over a wide age range (mean 52.4 yr). UTROSCTs often harbor translocations between ESR1 and nuclear receptor coactivators NCOA1-NCOA3. Here, we present a 21-yr-old woman with a 16 cm complex uterine mass on CT. Grossly, the tumor had an infiltrative appearance. Histologically, it consisted of mild to moderately atypical, spindled cells with ovoid nuclei, growing in fascicles and cords within fibrous to myxohyaline stroma, with tongue-like infiltration of the myometrium. Immunohistochemically, tumor cells were positive for AE1/AE3, ER, PR, vimentin, WT-1, and CD56, and negative for inhibin, calretinin, SMA, desmin, and CD10. Whole exome and whole transcriptome sequencing identified a pathogenic ESR1::CITED2 fusion. The tumor recurred twice (15 and 21 mo after initial surgery) in the abdomen and pelvis. Taken together, the findings suggest this tumor may represent a malignant UTROSCT variant with a novel translocation.
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