Differential expression of SOX2 and SOX17 in testicular germ cell tumors

Testicular germ cell tumors (GCTs) are subclassified to seminoma and nonseminomatous GCT for the purpose of treatment and prognostication. This study examined SOX2 and SOX17 expression patterns in a total of 67 cases, including 41 pure GCTs (32 seminomas and 9 embryonal carcinomas) and 26 mixed GCTs (9 foci of seminoma, 21 of embryonal carcinoma, 17 of yolk sac tumor, 19 of teratoma, and 5 of choriocarcinoma). All seminoma components showed diffuse SOX17 nuclear expression and were negative for SOX2. All but one of the embryonal carcinomas showed diffuse SOX2 nuclear expression with the one showing a focal reaction, whereas all were negative for SOX17. SOX17 was variably expressed in all yolk sac tumor components, but SOX2 was negative. Teratomas showed variable SOX2 and SOX17 expressions in the epithelial elements. Choriocarcinomas were negative for SOX2 and SOX17. SOX2 and SOX17 expression patterns can distinguish between seminoma and embryonal carcinoma, and this distinction may be diagnostically useful.