The answer depends on histological type of testicular cancer. For seminomas, which account for ~60% of testicular germ cell tumors (pure or mixed), OCT3/4 (POU5F1 gene) is one of the established antigens for diagnosis by immunohistochemistry. OCT3/4 is also expressed by embryonal carcinomas, which are found as a pure type or a component of testicular germ cell tumors (~40%).
Jones TD, Ulbright TM, Eble JN, Baldridge LA, Cheng L. OCT4 staining in testicular tumors: a sensitive and specific marker for seminoma and embryonal carcinoma. Am J Surg Pathol. 2004 Jul;28(7):935-40.