Sarcoma, or embryonal carcinoma, while being the most frequent malignant tumor affecting the human testis, is of especial interest when occurring in twins. To the pathologist and cancer research worker, particularly those studying the hereditary angle of such disease, this report may appeal strongly.
Identical or uniovular twins result from the fertilization of a single ovum by a sperm. In the process of embryonic development two individuals are produced instead of one, probably by an equal division of the blastoderm. They are enclosed in the same chorion, have the same placenta and are always of the same sex. It would appear that these individuals, developing as they do from an equal division of the blastoderm, might carry the same disease potentialities as well as the same physical characteristics. Moreover, tumors such as sarcomas, which are thought to arise from a fetal rest group of neoplastic tissue cells, might well have