Morphology and histogenesis of yolk sac tumors in the testis

The differentiation of yolk sac tumor cells was similar to the processes of development of embryonic and extraembryonic endoderm during the first 7 wk after cleavage. Two ways of yolk sac tumor histogenesis are discussed: differentiation of embryonal carcinoma cells, and redifferentiation of the polypotent undifferentiated anaplastic seminoma cells. Histogenesis features described may be responsible for aggressive nature and high malignancy of yolk sac tumors.