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Immature teratoma of the ovary with distant metastases: favorable prognosis and insights into chemotherapeutic retroconversion.

We present a case of a young woman with an immature teratoma of the right ovary that showed systemic metastases. The patient initially experienced abdominal distention at the age of 15 years. Radiographic assessment revealed a right ovarian tumor; thus, right salpingo-oophorectomy was performed, and the resected ovarian tumor showed a multilocular cystic lesion with partially solid areas. Pathologic diagnosis was an immature teratoma, grade 2. As brain, lung, and liver metastases were discovered within 2 years after the operation, sequential resections of the metastatic foci were performed before chemotherapy as well as during the early and late stages of chemotherapy. The resected specimens of each metastatic focus contained histologically more mature elements of the primary immature teratoma and exhibited a decrease in the Ki-67 labeling index, the later the resection was performed. As far as we know, this is the first case of brain metastasis stemming from an immature teratoma of the ovary. In addition, it was highly suggestive that chemotherapy itself was the main etiological factor for the promotion of maturation. The favorable prognosis of this malignant tumor even after brain metastasis was verified by the 10-year-survival of the patient.