‘Malignant transformation’ of mature cystic teratoma

Recently we observed an endometrioid carcinoma with clear cell changes in the background of an endometriotic cyst of the right ovary (T1c) adjacent to a mature cystic teratoma (MCT) in a 51-year-old woman. Minimal microscopic focus of grade 1 endometrioid adenocarcinoma confined to endometrium was found in the uterine corpus. We read with great interest two papers published in The Journal of Obstetrics and Gynaecology Research. Kim et al. described a case of synchronous mucinous adenocarcinoma (MA) and strumal carcinoid tumor from one of two ovarian MCT (one in each ovary) with synchronous cervical cancer. Ulker et al. reported six cases of malignant transformation arising from ovarian MCT. Histologically, three of six cases were squamous cell carcinomas, two cases were carcinoid tumors and one case was an MA. One case in the series reported by Ulker et al. has been reported in a previous paper that the authors did not cite. This case was an MA of the ovary arising in an MCT during pregnancy in a 38-year-old woman. The origin of MA from a teratomatous component has not been found. The malignancy found in an MCT may be considered of ‘teratomatous’ origin only when the following histological features are present: the continuity of cystic teratomatous epithelium with the adenocarcinoma and the strong unity of both components. MA in association with MCT may be a coincidental primary ovarian carcinoma of the surface epithelium rather than a neoplasm of teratomatous origin. In this case, the two neoplasms should be considered independent and the term ‘malignant transformation’ should be avoided. In the paper by Kim et al., the description of MA in MCT is very accurate and the two neoplasms may be considered of teratomatous origin. In the Results section of the paper by Ulker et al., the histology has not been described and the origin of malignancy from the teratomatous component is not documented. Consequently the term ‘malignant transformation’ is not justified.