Introduction/Background Immature ovarian teratomas are rare ovarian germ cell tumors mostly diagnosed in young women. They are associated with a variable potential of distant metastasis. According to current guidelines, recommended treatment is complete tumor resection, operative staging including peritoneal washing, omentectomy, peritoneal biopsies followed by postoperative chemotherapy- except in stage I.

Methodology A 29- year- old woman was referred to our department three months after left-sided salpingo-oophorectomy and complete staging procedure of an immature ovarian teratoma IA, grade 3 for which she did not receive additional chemotherapy. On routine clinical examination no local recurrence was detected but in radiological imaging bone metastasis in the right os sacrum and its surrounding tissue were confirmed. Being unresectable, the patient received radiotherapy.

Shortly thereafter a generalized metastasis of bones and lungs was diagnosed. At this time AFP was newly elevated to 159 U/ml. With disease progression and deteriorating general condition we were forced to apply high dose chemotherapy with stem cell harvesting. After three cycles PET-Scan showed no FDG-avid lesions and an AFP decrease to 13.2 U/ml. To date she is alive without relapse.

Results Histological examination of two different bone metastases revealed original immature teratoma showing the same characteristics like the initial histology. Though AFP was elevated at baseline and at the time of progression, yolk sac tissue was never confirmed in histological examination. Chromosome analysis and next generation sequencing was processed, but without any specific result. This was confirmed by reference pathology.

Conclusion To our knowledge this is the first case report of bone metastases developing from an immature ovarian teratoma FIGO Stage IA. As even early-stage immature ovarian teratomas are at risk to potentially develop metastasis a close and long term follow up monitoring of the patients is crucial. The importance of AFP in our patient remains unclear.

Disclosures None.