Atypical seminoma--histologic features, immunohistochemical characterization, and correlation with survival.

Classical seminoma and embryonal carcinoma are two points in the spectrum of histologic differentiation in testicular germ cell tumors. The validity of an intermediate category, ie, atypical seminoma (AS) is questionable. Histopathologic and clinical data on 42 patients treated for primary testicular germ cell tumor from 1975 to 1985 were reviewed. Twenty-seven cases were identified as classical seminoma and nine were embryonal carcinoma. The remaining six cases were somewhat problematic to classify, combining the growth pattern of seminoma with cytologic features of embryonal carcinoma. Immunocytochemically, four of these tumors suggested some progression towards the embryonal carcinoma phenotype on the basis of cytokeratin expression. Survival for classical seminoma, AS, and embryonal carcinoma were 90%, 80%, and 63% respectively (mean follow-up, 8.6 years). Although the survival differences were not statistically significant, when considered with morphologic and selected immunocytochemical data, they tend to support the concept of an AS as an intermediate lesion between classical seminoma and embryonal carcinoma.