[Malignant sacrococcygeal teratoma in an adult woman].

Background: Sacrococcygeal teratomas are neoplasms that are ordinarily diagnosed intrauterinely. In case of complete or partial intrapelvic sacrococcygeal teratoma, it may happen that it is only ascertained at a later age.
Case Description: During a regular monitoring visit for breast cancer a 58-year-old female reported that she had discovered a swelling at the level of her coccyx. MRI imagery appeared to indicate an ectopic ovary. After resection, it appeared that it was a mature teratoma from which mucinous adenocarcinoma had developed.
Conclusion: Given the risk of malignant deterioration, it is important that sacrococcygeal teratoma be recognized and treated by means of complete resection, including resection of the coccygeal bone.