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. It has been found in association with Klinefelter syndrome. References

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Germ cell neoplasia
Gynaecological neoplasia