p53 and MDM2 expression in primary and metastatic testicular germ cell tumors: Association with clinical outcome

Several recent studies have suggested that testicular germ cell tumors express high levels of wild-type p53 protein. To clarify and confirm this unexpected result, we have investigated seminomatous and nonseminomatous germ cell tumors at the genomic, mRNA, and protein levels. Thirty-five tumors were examined for p53 overexpression using antibodies directed against the p53 (PAb1801, PAb240, and CM1), mdm2 (IF2), and p21Waf1/Clp1 (EA10) proteins. Thirty-two tumors were screened for p53 mutations by single-strand conformation polymorphism analysis. Eighteen tumors were screened with a functional assay that tests the transcriptional competence of human p53 protein expressed in yeast. On frozen sections, 100, 65, 35, 73, and 0% of tumors reacted with the CM1, PAb240, PAb1801, IF2, and EA10 antibodies, respectively. No p53 mutations were detected by single-strand conformation polymorphism or by functional assay. The fact that many tumors overexpress wild-type p53 but not mdm2 rules out mdm2 overexpression as a general explanation for the presence of wild-type p53 in these tumors. The absence of p21 overexpression suggests that p53 may be unable to activate transcription of critical target genes, which may explain why the presence of wild-type p53 is tolerated in this tumor type, although the mechanism for this transcriptional inactivity remains to be established.

Testicular cancer is a relatively rare neoplasia, with an incidence of about 1,5% among male malignancies, usually in the third and fourth decade of life. Although several histological variants are known, with some histotypes affecting older patients (e.g., spermatocytic seminoma), there is a clear predominance (90-95%) of germ cell tumors among young adults patients1. Testicular Germ Cell Tumor (TGCT), undoubtedly the seminoma histological variant more than non-seminoma one, is definitely a highly curable disease, with a distinctive sensitivity to cisplatin-based therapy (and for seminomas to radiotherapy) and an outstanding cure rate of nearly 80% even for patients with advanced disease. So far, clinical and pathohistological features supported our efforts to choose the best treatment option for patients suffering from this malignancy, but we don't clearly enough know molecular and pathological features underlying different clinical behaviors, mostly in early-stage disease: by improving this knowledge, we should better "shape" therapeutic or surveillance programs for each patient, also in order to avoid unnecessary, if not harmful, treatments.

Various prognostic factors have been investigated in order to predict the minority of male germ cell tumor (GCT) patients who will develop resistant disease. However, no prognostic system has been proven accurate. Paraffin-embedded tissue specimens, obtained from primary lesions during the initial diagnosis of 83 advanced chemotherapy-treated GCT male patients, were stained for 7 immunohistochemical markers: p53, bax, bcl-2, MIB-1, topoisomerase IIa, c-kit and COX-2. The percentage of positive cells for each marker was measured for each patient. Cox regression was used for the prognostic factor analysis. All patients were followed for a median of 4 years. Nineteen patients had seminoma and 64 non-seminomatous GCT. In univariate analysis, only p53 (hazard ratio (HR) = 4.01, 95% confidence interval (CI) = 1.25-12.84, p = 0.019) and MIB-1 (HR = 3.16, 95% CI = 1.06-9.45, p = 0.039) were found to be prognostic for disease-specific survival. The best prognostic cut-off values of p53 and MIB-1 were 10% and 30% respectively. In multivariate analysis, these two markers obtained independent significance only when considered in combination (HR = 6.63, 95% CI = 1.40-31.41, p = 0.017, for patients with one or both markers above their cut-off), while the International Germ Cell Consensus Cancer Group (IGCCCG) risk was the most significant (HR = 7.99, 95% CI = 1.96-32.52, p = 0.004, for the high-risk group). However, the expression of these markers seemed to be significantly correlated with known prognostic factors. Nevertheless, we identified 34 patients of low IGCCCG risk expressing both markers below their cut-off with excellent survival. Among 7 immunohistochemical markers, p53 and MIB-1 demonstrated prognostic significance. Their combination may contribute to improvement of the accuracy of the currently approved prognostic system (IGCCCG).