[Malignant transformation in mature sacrococcygeal teratoma in an adult patient].

Teratomas are tumors derived from two or more of the germ layers. They are more frequent in childhood than in adulthood and are predominant in women. Although they usually originate in the ovaries, there are other less frequent locations. The sacrococcygeal location is rare, observed in 1:40 000 births. Although most are benign, up to 2% may present malignant transformation. We present the case of a 60-year-old woman with a history of en bloc resection of a presacral pelvic tumor whose pathology reported a mature teratoma. After 2 years she developed sacrococcygeal pain. Imaging studies revealed a 6 cm tumor with bone involvement of the last sacral vertebrae. A core needle biopsy was performed, which reported recurrence of mature teratoma. After staging, which did not show systemic disease, she was evaluated by a multidisciplinary committee and surgical resection was indicated. An en bloc resection consisting of distal sacrectomy at the level of S3 and surrounding muscles was performed. The pathological report confirmed the presence of a mature teratoma with malignant transformation to colorectal adenocarcinoma, with negative margins. After multidisciplinary evaluation a strict follow-up without adjuvant treatment was indicated. The patient remained disease-free for 24 months, after which she presented impairment in performance status with systemic progression, passing away 2 months later. Sacrococcygeal teratomas are uncommon tumors. Malignancy is a rare event and complete resection is the treatment of choice.