Undifferentiated intratubular germ cell tumor of the testis: light and electron microscopic study of a unique case.

A 34-year-old white man was found to have a nodule on the surface of right testis which turned out to be metastatic embryonal carcinoma within the tunica albuginea. Examination of the orchiectomy specimen revealed extensive undifferentiated intratubular germ cell tumor (carcinoma in situ) with foci of intratubular embryonal carcinoma and seminoma. Ultrastructure of the cells comprising the carcinoma in situ was similar to that of undifferentiated germ cells. The development of intratubular embryonal carcinoma and seminoma in a testis with extensive carcinoma in situ lends further support to the concept that carcinoma in situ or the testis represents an undifferentiated germ cell tumor from which other types of germ cell tumors of the testis may evolve.