The value of SOX2 in the differential diagnosis of SMARCA4 (BRG1)-deficient uterine neoplasms

SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily A, member 4 (SMARCA4/BRG1)-deficient undifferentiated uterine sarcoma (SDUS) is a recently described uterine sarcoma. It is characterized by predominantly rhabdoid or large epithelioid cells with abundant cytoplasm and varying components of small and spindle cells, resembling the 'large cell variant' of small cell carcinoma of the ovary, hypercalcemic type (SCCOHT). In addition, SMARCA4-inactivating mutations have been described as the driver mutations in SDUS. However, undifferentiated endometrial carcinoma (UDEC) and dedifferentiated endometrial carcinoma (DDEC) may show some clinical and morphological overlaps with SDUS, and about 20% of reported UDEC/DDEC cases also have loss expression of SMARCA4. SDUS is a very aggressive disease and universally lethal in all reported cases. Differentiating SDUS from UDEC/DDEC is relevant for the prognosis, pathogenesis, and possible targeted therapies for the disease. In this study, we compared the clinical, morphological, immunohistochemical, and molecular characteristics of 10 tumors including 2 SDUS, 2 SCCOHT, 1 uterine carcinoma with neuroendocrine differentiation (UDEC?), and 5 UDEC/DDEC. All 5 UDEC/DDEC cases showed strong and diffuse nuclear positivity for SOX2, while all SCCOHT and SDUS cases were completely negative. We concluded that SOX2 could be a useful marker for the