SOX17 is a highly sensitive and specific marker for metastatic ovarian and endometrial carcinomas in cytology cell block specimens

Background: SOX17 (SRY-box transcription factor 17) was recently identified as a highly sensitive and specific marker for ovarian and endometrial carcinomas in surgical specimens. In this study, validation of the utility of SOX17 immunohistochemistry (IHC) in diagnosing metastatic gynecologic carcinomas in cytology specimens was sought. Methods: The study cohort included 84 cases of metastatic carcinomas that included 29 metastatic gynecologic carcinomas (24 ovarian high-grade serous carcinomas, two endometrial serous carcinomas, one low-grade serous carcinoma, one ovarian clear cell carcinoma, and one endometrial endometrioid carcinoma) and 55 cases of metastatic nongynecologic carcinomas (10 clear cell renal cell carcinomas, 10 papillary thyroid carcinomas, 11 gastrointestinal adenocarcinomas, 10 breast carcinomas, 10 lung adenocarcinomas, and four urothelial carcinomas). Cytology specimen types included peritoneal fluid (n = 44), pleural fluid (n = 25), and fine-needle aspiration (n = 15). SOX17 IHC was performed on the cell block sections. The intensity of staining and percent positivity of the tumor cells were evaluated. Results: SOX17 was highly expressed in all tested metastatic gynecologic carcinomas with diffuse and strong nuclear expression (29 of 29; 100%). SOX17 was negative in other metastatic nongynecologic carcinomas (54 of 55; 98.18%) except for one papillary thyroid carcinoma that showed low positivity (<10%). Conclusions: SOX17 is a highly sensitive (100%) and specific (98.2%) marker for the differential diagnosis of metastatic gynecologic carcinomas in cytology specimens. Therefore, SOX17 IHC should be included in the workup of differential diagnosis of metastatic gynecologic carcinomas in cytology specimens.