polyembryoma polyembryoma polyembryoma is a rare, very aggressive form of germ cell tumor usually found in the ovaries. polyembryoma has features of both yolk sac tumour and undifferentiated teratoma/embryonal carcinoma, with a characteristic finding of embryoid bodies lying in a loose mesenchymal stroma. polyembryomapolyembryoma of the ovary, h&e stainspecialtyoncology, gynecology it has been found in association with klinefelter syndrome.