We evaluated p53 expression and tumor proliferative activity (TPA) using monoclonal antibodies to Ki-67 and proliferating cell nuclear antigen (PCNA) in 26 patients with seminomatous and nonseminomatous testicular germ-cell tumors (GCTs). Correlation between p53 expression and TPA, as well as the clinical correlation with the expression of these proteins were also assessed. There were eight cases of pure seminoma and 18 cases of nonseminomatous GCTs, collectively consisting of 45 tumors or tumor components. The nonseminomatous GCTs were mixed or pure and included choriocarcinoma (CC), embryonal carcinoma (EC), immature teratoma (IMT), mature teratoma (MT), seminoma, and yolk sac tumor (YST). The ages of the patients with seminomatous GCTs ranged from 24 to 47 years (mean, 34 years) and those for patients with nonseminomatous GCTs ranged from 17 to 43 years (mean, 29 years). Sixteen (44%) of the 36 nonseminomatous GCTs or tumor components were positive for p53 protein. Ten (91%) of eleven ECs, three (38%) of eight YSTs, two (20%) of ten MTs, and the single case of CC were positive for p53 protein. All nine seminomas and three of six IMTs were only focally positive for p53 protein. The p53 expression in ECs and YSTs was significantly higher than that in IMTs, MTs, and seminomas (P=0.0001). TPA was present in the majority of the seminomatous and nonseminomatous GCTs, and was significantly higher in ECs and YSTs than in seminomas, MTs, and IMTs (Ki-67, P=0.0001; PCNA, P=0.0006). In the majority of the cases PCNA expression was higher than Ki-67 expression (P=0.0001). The mean TPA percentage was significantly higher in the p53-positive tumors or tumor components (EC and YST) when compared with the mean TPA percentage in those neoplasms that were focally positive or negative for p53 protein (Ki-67, P=0.003; PCNA, P=0.046). p53 expression was also associated with histologically aggressive tumors (ECs and YSTs) that also exhibit high TPA. No relationship appears to exist between the three tumor markers and the clinical stage or the patients' follow-up and outcome in this small series. Further studies are necessary to elucidate the roles of p53 and proliferation markers in testicular tumorigenesis and as prognostic markers.

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