Endometrial stromal tumors are rare lesions with a diverse morphology, which may make achieving the correct diagnosis challenging in some cases. We report a case of a uterine mesenchymal tumor diagnosed as endometrial stromal nodule with a peculiar whorled morphology and GREB1::CTNNB1 fusion confirmed by transcriptome RNA sequencing. The tumor was sharply demarcated, lacked invasive growth, and had benign behavior, as the patient remained without disease recurrence 15 years later. Immunohistochemically, the tumor cells showed diffuse nuclear expression of beta-catenin, confirming the activation of the beta-catenin pathway. Our case represents only the 4th reported case of CTNNB1-rearranged endometrial stromal tumor with extensive whorling. The biological nature of uterine tumors characterized by whorled morphology and rearrangement of CTNNB1 is not yet clear, which underscores the importance of genetic profiling for accurate diagnosis and potential targeted therapies in malignant cases.

• Keywords
• ESN, Endometrial stromal tumors, GREB1, GREB1::CTNNB1 fusion, Uterine mesenchymal tumors,
• Publication type
• Journal Article MeSH

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 manner, 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, morphologic, 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 coexpression of sex cord-stromal, smooth muscle, and epithelial markers, as well as hormone receptors. Next-generation sequencing 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 with 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 2 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.

• Keywords
• ESR1, GREB1, NCOA1-3, UTROSCT, expression profiling, immunohistochemistry, molecular testing, uterine tumor resembling ovarian sex cord tumors,
• MeSH
• Adult MeSH
• Sex Cord-Gonadal Stromal Tumors * genetics   pathology   MeSH
• Immunohistochemistry * MeSH
• Nuclear Receptor Coactivator 2 genetics   MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Biomarkers, Tumor * genetics   analysis   MeSH
• Uterine Neoplasms * genetics   pathology   MeSH
• Ovarian Neoplasms genetics   pathology   MeSH
• Aged MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Nuclear Receptor Coactivator 2 MeSH
• Biomarkers, Tumor * MeSH
• NCOA2 protein, human MeSH Browser