B72.3 serves as a new diagnostic marker for testicular Leydig cell tumor.

Leydig cell tumors (LCTs) and Sertoli cell tumors (SCTs) are the two most common sex cord-stromal tumors of the testis, and can exhibit overlapping histologic and immunophenotypic features, creating diagnostic challenges. Currently, differential diagnosis of these two tumors relies primarily on histological features, with no reliable immunohistochemical markers available. B72.3 is a widely used immunohistochemical antibody recognizing tumor-associated glycoprotein 72 (TAG-72) expressed in a broad range of normal and tumor tissues. Incidentally, we observed that B72.3 specifically stains the Leydig cells, but not Sertoli cells, in normal testis, suggesting its potential utility as a diagnostic marker for testicular LCTs. In this study, we identified 35 patients with testicular LCTs (primary: n = 28; metastatic: n = 7) and 12 with testicular SCTs (primary: n = 10; metastatic: n = 2). B72.3 immunohistochemistry was performed on 17 testicular LCTs and 7 SCTs. Positive B72.3 staining was observed in 9 of 17 LCTs (53 %), including 8 of 12 primary tumors (67 %) and 1 of 5 metastatic tumors (20 %). Among the positive LCTs, 2 exhibited diffuse staining, 2 showed patchy positivity, and 5 had focal staining. By contrast, all 7 SCTs and 1 Sertoli cell nodule were negative for B72.3. These findings indicate that B72.3 may serve as a useful diagnostic marker for testicular LCTs and can aid in distinguishing LCTs from SCTs in challenging cases.