Malignant steroidogenic tumor arising from sacrococcygeal mature teratoma.

We report a case of malignant steroidogenic tumor arising from a sacrococcygeal teratoma in a 5-year-old girl. A congenital gluteal mass and a 7-month history of precocious puberty had been noted, and a large estrogen-producing tumor in the sacrococcygeal area was found. After a biopsy, chemotherapy and tumor resection were performed, and no recurrence has been observed. The biopsy specimen showed small clusters of atypical round cells adjacent to a mature teratoma. They had large round nuclei with prominent nucleoli and abundant eosinophilic cytoplasms and were positive for vimentin, steroidogenic factor-1, inhibin α, and melan-A. Increased mitoses, vascular invasion, and necrosis were noted. The tumor was diagnosed as sacrococcygeal mature teratoma, with malignant steroidogenic tumor as somatic malignant transformation. Although several kinds of somatic malignant transformation of sacrococcygeal teratoma have been reported, to the best of our knowledge, this is the first case of malignant steroidogenic tumor arising from sacrococcygeal teratoma.