SOX17 expression in mesonephric-like adenocarcinomas and mesonephric remnants/hyperplasia of the female genital tract: Expanding its utility as a Müllerian biomarker

Aims: Recently, SOX17 has emerged as a promising biomarker for non-mucinous M & uuml;llerian (ovarian and endometrial) carcinomas, demonstrating increased specificity in comparison to PAX8 while maintaining similar sensitivity. However, expression of SOX17 in mesonephric-like adenocarcinoma (MLA), a carcinoma of the female genital tract with uncertain, but probably M & uuml;llerian histogenesis, remains unexplored. This study aims to address this gap. Methods and results: SOX17 immunohistochemistry was performed on whole tissue sections from 68 MLAs originating from the endometrium or ovary and seven cervical mesonephric carcinomas, as well as six mesonephric remnants/hyperplasias. Using a four-tiered scoring system based on distribution and intensity of staining, 68% of MLA displayed a negative/low (< 10%) SOX17 expression pattern, which contrasts with the high expression observed in most M & uuml;llerian carcinomas. However, 22% of MLA demonstrated high SOX17 expression, similar to other endometrial and ovarian carcinomas. Similarly, five of seven (72%) mesonephric carcinomas of the cervix were SOX17-negative, but two cases (28%) were positive. All mesonephric remnants/hyperplasias were SOX17 negative. Conclusions: The majority of MLA are negative or exhibit low SOX17 expression, in contrast to the diffuse and strong expression commonly seen in other types of M & uuml;llerian carcinoma. However, a subset of MLAs demonstrate high SOX17 expression. Therefore, absence of SOX17 staining is supportive for MLA when the differential includes another non-mucinous M & uuml;llerian carcinoma. SOX17 may also be useful for differentiating mesonephric remnants/hyperplasias from M & uuml;llerian malignancies and benign M & uuml;llerian glandular lesions.