Background: Carcinoma in situ (CIS) is regarded as the precursor of all histologic variants of testicular germ cell tumors except spermatocytic seminoma. For a variety of human malignancies, alterations of the p53 tumor suppressor gene have been identified as prognostic factors for a poor clinical course. Discussions of the occurrence of p53 gene alterations in testicular carcinoma have been controversial. Immunohistochemical detection of the p53 oncoprotein has been reported in four of eight CIS cell areas adjacent to mature teratoma. The majority of investigations have failed to demonstrate p53 gene alterations on the DNA level in testicular carcinoma specimens. However, the genetic analysis of testicular carcinoma is complicated by the histologic variety of tumors, resulting in a mixture of subtypes undergoing moleculargenetic analysis. In the present study, CIS cells identified in normal testicular tissue adjacent to different testicular tumors were examined for alterations of the p53 tumor suppressor gene. The authors believed that the detection of p53 alterations in CIS of the testis would not only support the idea of malignant potential in CIS but might also demonstrate the involvement of the p53 tumor suppressor gene in the development of germ cell cancers.
Methods: CIS cells were identified in the normal testicular tissue adjacent to 18 seminomatous and nonseminomatous germ cell tumors by histopathologic criteria and the immunohistochemical staining reaction for placental-like alkaline phos phase, a highly specific marker for testicular CIS. About 20-50 CIS cells per tumor were collected by a microdissection technique and were subjected to RNA. SSCP analysis and additional DNA-sequence analysis.
Results: In 12 of 18 cases (66%), RNA-SSCP analysis of the microdissected CIS cells revealed mutational band shifting at the p53 gene locus. In 7 of 18 cases (39%). the results of SSCP analysis were confirmed by DNA sequencing. DNA-sequence analysis revealed missense point mutations in the p53 gene in four cases (exon 5, codons 158, 170, and 176; exon 6, codon 213) and silent mutations in two cases (exon 5, codon 178; exon 6, codon 213). In one case, the identical missense point mutation (exon 5, codon 176) was detected in the CIS cells and also in the associated germ cell tumor. In two of six cases, different mutations were found in the CIS cells and the testicular tumor. In three cases in which DNA sequencing revealed point mutations in CIS cells, alterations of the p53 gene could not be detected in the examination of the associated tumor specimen.
Conclusions: These findings appear to support the concept that malignant biologic characteristics are present in the in situ stage of testicular germ cell tumors. This is the first report demonstrating monoclonal development of a manifested testicular carcinoma from associated CIS cells on the basis of a certain mutational event in the p53 gene sequence. The involvement of p53 gene alterations in precursor cells of testicular carcinoma appears likely.