Utility of SOX17 Immunohistochemical Stain in Serous Fluid Cytology Cell Block Specimens

The identification of metastatic tumors in serous fluid cytology specimens (SFCS) has always been a challenge. In this study, we explored SOX17 as an immunohistochemical (IHC) marker for the diagnosis of metastatic gynecologic tumors in body fluid specimens.

We selected 97 tumor cases, including 85 SFCS with adequate cell block material (from gynecologic primary, n = 30 and others, n = 55) and 12 histology specimens (thymic and thyroid tumors). SOX17 IHC was performed on all selected cases, and results were interpreted as positive or negative. Positive results were further characterized by intensity (nuclear staining) as weak (1+), moderate (2+), and strong (3+) and percentage of positive cells as focal (< 10%), patchy (10%-50%) and diffuse (> 50%).

In SFCS of gynecologic primary tumors, SOX17 exhibited strong nuclear staining in 28 out of 30 tumors, with two cases showing moderate staining. All non-gynecologic metastatic tumors in effusion cytology specimens were SOX17-negative except for one case of renal cell carcinoma, which displayed a moderate patchy staining pattern. All histology cases consisting of thymic and thyroid tumors were negative for SOX17.

In this study, all tumors of gynecologic tract origin in effusion SFCS were SOX17 positive, while all other non-gynecologic tumors were negative for SOX17 except for one case. This finding suggests that SOX17 IHC is an excellent addition to the IHC panel while working up tumors at metastatic sites, specifically when gynecologic primary tumors are in the differential diagnosis.