ALTERATIONS OF THE P53 TUMOR-SUPPRESSOR GENE IN CARCINOMA IN-SITU OF THE TESTIS

BACKGROUND. Carcinoma in situ (CIS) is regarded as the precursor of al l histologic variants of testicular germ cell tumors except spermatocy tic seminoma. For a variety of human malignancies, alterations of the p53 tumor suppressor gene have been identified as prognostic factors f or a poor clinical course. Discussions of the occurrence of p53 gene a lterations in testicular carcinoma have been controversial. Immunohist ochemical detection of the p53 oncoprotein has been reported in four o f eight CIS cell areas adjacent to mature teratoma. The majority of in vestigations have failed to demonstrate p53 gene alterations on the DN A level in testicular carcinoma specimens. However, the genetic analys is of testicular carcinoma is complicated by the histologic variety of tumors, resulting in a mixture of subtypes undergoing moleculargeneti c analysis. In the present study, CIS cells identified in normal. test icular tissue adjacent to different testicular tumors were examined fo r alterations of the p53 tumor suppressor gene. The authors believed t hat the detection of p53 alterations in CIS of the testis would not on ly support the idea of malignant potential in CIS but might also demon strate the involvement of the p53 tumor suppressor gene in the develop ment of germ cell cancers. METHODS. CIS cells were identified in the n ormal testicular tissue adjacent to 18 seminomatous and nonseminomatou s germ cell tumors by histopathologic criteria and the immunohistochem ical staining reaction for placental-like alkaline phosphatase, a high ly specific marker for testicular CIS. About 20-50 CIS cells per tumor were collected by a microdissection technique and were subjected to R NA-SSCP analysis and additional DNA-sequence analysis. RESULTS. In 12 of 18 cases (66%), RNA-SSCP analysis of the microdissected CIS cells r evealed mutational band shifting at the p53 gene locus. In 7 of 18 cas es (39%), the results of SSCP analysis were confirmed by DNA sequencin g. DNA-sequence analysis revealed missense point mutations in the p53 gene in four cases (exon 5, codons 158, 170, and 176; exon 6, codon 21 3) and silent mutations in two cases (exon 5, codon 178; exon 6, codon 213). In one case, the identical missense point mutation (exon 5, cod on 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 seque ncing revealed point mutations in CIS cells, alterations of the p53 ge ne could not be detected in the examination of the associated tumor sp ecimen. CONCLUSIONS. These findings appear to support the concept that malignant biologic characteristics are present in the in situ stage o f testicular germ cell tumors. This is the first report demonstrating monoclonal development of a manifested testicular carcinoma from assoc iated CIS cells on the basis of a certain mutational event in the p53 gene sequence. The involvement of p53 gene alterations in precursor ce lls of testicular carcinoma appears likely. (C) 1996 American Cancer S ociety.