Background: It has been suggested that tumorigenesis of the germ cell tumor of the testis includes abnormal and developmentlike differentiation of primordial germ cells to several mature type tumors.
Methods: To clarify roles of protooncogenes in the unique tumorigenic mechanism in the human germ cell tumor, the authors examined the expression of 15 protooncogenes in human primary germ cell tumors of the testis with Northern blot analyses.
Results: Fifteen (94%) of 16 seminomas and 5 (83%) of 6 embryonal carcinomas had a significant levels of N-myc expression, whereas they did not express two receptor type protooncogenes, c-erbB-1 and c-erbB-2. In contrast, some immature teratomas had a high level of c-erbB-1 expression, and an advanced case showed a significant level of c-erbB-2 expression. Immature teratomas did not show N-myc expression. Higher levels of c-mos expression were observed in several cases of seminomas and embryonal carcinomas. Expression of c-Ki-ras or N-ras was observed in all histologic subgroups and normal testes.
Conclusion: A significant level of N-myc expression may be essential for undifferentiated tumors including seminoma and embryonal carcinoma, whereas c-erbB-1 and possibly c-erbB-2 may have important roles in the differentiated tumors such as immature teratoma. These results suggest that some of the protooncogene expression may be switched critically during the differentiation from seminomas or embryonal carcinomas to the more differentiated-type tumor.