Disseminated Metastasis after Resection of Sacrococcygeal Teratoma with Mucinous Adenocarcinoma: A Case Report

Mature teratoma is a common tumor that can undergo malignant transformation, either in ovarian or extragonadal sites. While adenocarcinoma superimposed on sacrococcygeal teratoma is rare, mucinous variants have been reported in only five cases. Here, we present a case of a young girl with disseminated metastasis of mucinous carcinoma, initially of unknown primary origin. Further investigation by a dedicated multidisciplinary team (MDT) revealed a focus of mucinous carcinoma (intestinal type) in a sacrococcygeal teratoma incompletely resected five years earlier. The patient is currently undergoing second-line chemotherapy after experiencing side-effects on the first-line regimen. Pathologists, gynecologic oncologists, and surgical oncologists should exercise caution when dealing with locally aggressive teratomas, thoroughly searching for malignant components and conducting short-term follow-up.