Testosterone in infant testis yolk sac tumor indicating a mixture of germ cell and sex cord/stromal elements: a new concept.

The presence of testosterone in yolk sac tumor of the infant testis was investigated immunohistochemically. All 16 cases tested were positive for the hormone. The antigen-positive tumor cells were primitive mesenchymal cells and columnar cells forming small ducts, which resembled Leydig cells and Sertoli cells, respectively. These cells accounted for about 1 to 20% of tumor cells and were intermingled with typical yolk sac structures. In contrast, no yolk sac tumor of adult testis was definitely positive for the antigen. In view of its distinctive histological and immunohistochemical features and clinical behavior, yolk sac tumor in the infant testis is most likely a separate and specific entity, composed of a mixture of germ cell and sex cord stroma derivatives.