Uterine tumors resembling ovarian sex cord tumors (UTROSCT) are rare neoplasms that typically follow a benign course. However, metastasis occurs in rare cases and features associated with poor outcomes are only recently being described. These include: size >
5 cm, at least moderate cytologic atypia, >
3 mitosis per 10 high-powered fields, infiltrative borders, necrosis, GREB1 rearrangements, ESR1 rearrangements, and NCOA2/3 fusions. To our knowledge, prominent sclerosis has not been described in UTROSCT, nor has it been associated with an increased risk of metastasis. We present the case of a 51-yr-old woman with UTROSCT with corded/trabecular growth and sclerosis. The presence of sclerosis resulted in the misdiagnosis of her uterine tumor as leiomyoma and her lung metastasis as sclerosing epithelioid fibrosarcoma. The correct diagnosis of UTROSCT with lung metastasis was reached upon a morphologic comparison of the primary and metastatic tumors and the performance of a broad panel of immunohistochemical stains revealing the tumor to be CD99, CD56, ER, and inhibin positive and negative for rearrangements in 138 targeted genes, including genes commonly described as rearranged in endometrial stromal sarcomas, Ewing sarcoma and sclerosing epithelioid fibrosarcoma. The panel did not include GREB1 or ESR or NCOA3, but NCOA1/2 rearrangements were not detected. Our case highlights the diagnostic dilemma introduced by the presence of sclerosis in UTROSCT. We suspect prominent sclerosis may be another feature predictive of malignant potential in UTROSCT.