Unraveling the molecular landscape of UTROSCT: Insights from a clinicopathological, morphological, immunohistochemical, and molecular analysis of 35 cases.

Abstract Uterine tumor resembling ovarian sex cord tumor (UTROSCT) is a rare tumor of uncertain lineage and low malignant potential. Most tumors behave in a benign fashion, but a subset of UTROSCT exhibit an aggressive clinical course with recurrences and metastases. The recurrent molecular alterations in UTROSCT mostly represent gene fusions involving NCOA1-3. We performed a comprehensive clinicopathological, morphological, immunohistochemical, and molecular analysis on a cohort of 35 UTROSCT. The tumors exhibited various architectural patterns (diffuse, corded/trabecular, tubular, sertoliform, fascicular, whorled, nested, microfollicular, and pseudoglandular), often in combination. The immunohistochemical analysis confirmed the polyphenotypic immunoprofile, often with co-expression of sex cord-stromal, smooth muscle, and epithelial markers, as well as hormone receptors. NGS RNA analysis revealed recurrent NCOA1-3 gene fusions in 22/32 analyzed cases (69%), including ESR1::NCOA3 (11/22), GREB1::NCOA2 (7/22), ESR1::NCOA2 (3/22), and GREB1::NCOA1 (1/22). Tumor mutation burden was low in all cases. The fusion-positive cases exhibited statistically significant association with whorled architecture, conversely necrosis was associated with fusion-negative status. We did not find a significant relationship between any architectural pattern and GREB1-alterations, but the NCOA2-altered tumors were associated with pseudoglandular architecture. The GREB1-altered cases occurred in older patients and tended to be more often intramural masses compared to ESR1-altered cases. On the contrary, the ESR1-altered cases presented more often like submucosal or polypoid tumors. Two tumors exhibited aggressive behavior with recurrent disease. Both of these cases harbored a GREB1::NCOA2 fusion. Unsupervised hierarchical cluster analysis of our cohort revealed two main clusters. The tumors with GREB1 or NCOA2 fusion cluster together, suggesting that there are underlying molecular differences between these cases and cases with ESR1::NCOA3 fusion or without fusion. Our findings contribute to the growing knowledge about a rare neoplasm with currently uncertain biological behavior.