The incidence of yolk sac tumor (endodermal sinus tumor) elements in germ cell tumors of the testis in adults.

The incidence of yolk sac tumor (endodermal sinus tumor) elements was studied in 147 germ cell neoplasms of the testis in adults observed over a 4 1/2-year period. Excluding 79 cases of pure seminoma, yolk sac tumor elements were found in 26 (38%) of 68 tumors; in 8 tumors the yolk sac tumor was the predominant element. Yolk sac tumor elements were found admixed with all other germ cell tumor elements. Tumors composed entirely of yolk sac tumor were not encountered. Fifteen (57%) of the 26 patients with tumors containing yolk sac tumor elements have died of their disease during the period under study, compared with 13 (31%) of the remaining 42 patients, suggesting that the prognosis of adults with testicular tumors containing yolk sac tumor elements is unfavorable. This is in contrast to the relatively good prognosis of infants and young children with testicular yolk sac tumor, and similar to the prognosis of female patients with ovarian yolk sac tumor. The results of the present study give further support to the view that yolk sac tumor (endodermal sinus tumor) is not adistinctive neoplasm of the infant's testis, but a germ cell neoplasm differentiating in the direction of yolk sac or vitelline structures, and occurring in the testis, ovary and extragonadal sites in common with other germ cell neoplasms.