Polyembryoma of the testis: a report of two cases dominant within mixed germ cell tumors and review of gonadal polyembryomas.

Two testicular mixed germ cell tumors, from men of 21 and 41 years, in which polyembryoma predominated are described. A literature review uncovered an additional five testicular and nine ovarian cases. One tumor occurred in a 60-year-old man, but all others occurred within the typical age range of gonadal germ cell tumors. One male presented with gynecomastia and one female with sexual precocity, but all otherwise had standard clinical manifestations. These tumors are typically large with non-specific gross features, but a few have a prominent hemorrhagic appearance. No tumor is known to have been entirely composed of embryoid bodies, the unit upon which the diagnosis of polyembryoma is based. The most common additional germ cell tumor component is teratoma, present in the great majority of cases, with an approximately equal smaller number of tumors being associated with embryonal carcinoma and yolk-sac tumor, manifest as overgrowths of these elements, derived from the parent epithelium within the embryoid body. Rarely there is choriocarcinoma, and syncytiotrophoblast and hepatoid cells are occasionally present. The microscopic features of the tumors vary according to the arrangement of embryoid bodies with other elements, the prominence of associated typically myxoid to edematous stroma, and the degree to which embryoid bodies are perfectly or imperfectly formed. Although its presence in a gonadal mixed germ cell tumor is probably not associated with any special behavior, its unique features should result in polyembryoma being recorded, particularly when present in significant amount. Furthermore, awareness of its features may facilitate recognition, particularly when seen at metastatic sites or extra-gonadal sites of primary germ cell neoplasia. Whether polyembroma should be considered a distinctive pattern of mixed germ cell neoplasia or a particular variant of high-grade immature teratoma is considered, herein, and arguments can be made in favor of each viewpoint.