Objectives: Inhibitors of topoisomerase II alpha (TopoIIα), an enzyme with a crucial role in DNA maintenance, are included in the chemotherapy protocols for testicular germ cell tumors (GCTs). Despite the success of current chemotherapy regimens, a significant number of patients experience relapse. We analyzed TopoIIα expression in primary and metastatic testicular GCTs because this enzyme is a target for some antineoplastic agents. Methods: Primary GCT specimens from 109 patients, including 57 seminomas and 52 mixed GCTs (41 embryonal carcinomas, 23 yolk sac tumors, 19 seminomas, 8 choriocarcinomas, 17 teratomas with immature elements, and 16 teratomas with mature elements), were obtained from our archives. The metastatic lesions from 11 of the patients with mixed GCTs included seven teratomas with mature components, five embryonal carcinomas, one yolk sac tumor, one choriocarcinoma, and one teratoma with immature components. Representative sections were subjected to immunohistochemistry with monoclonal antibody against TopoIIα, and the nuclear staining findings were evaluated. Results: Most embryonal carcinoma (100%), yolk sac tumor (95%), seminoma (88%), and choriocarcinoma (62%) components of the GCTs were TopoIIα immunoreactive. None of the teratoma specimens with mature elements expressed TopoIIα. Conclusions: The results of our study have shown that TopoIIα is expressed in most seminomas, embryonal carcinomas, yolk sac tumors, and choriocarcinomas, suggesting a possible mechanism of sensitivity of these components to TopoIIα inhibitors. Teratomas with mature and immature elements expressed low levels of TopoIIα, which might contribute to their chemoresistance. These findings imply that the variable chemoresponsiveness of testicular GCTs could have an underlying molecular basis.
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