Background: Vaginal carcinoma represents 1-2% of all gynecologic malignancies. Most cases reported secondary involvement from adjacent organs including cervix, uterus, and colorectum. Vaginal involvement from adenocarcinoma arising in mature cystic teratoma (MCT) has never been reported.
Case: A 29-year-old female presented with postcoital vaginal bleeding. She had had a history of right ovarian adenocarcinoma arising in MCT, FIGO stage IC, for 18 months’ duration. Incisional biopsy of the vaginal lesion revealed adenocarcinoma, morphologically and immunohistologically identical to the right oophorectomized specimen. She received three courses of paclitaxel and carboplatin chemotherapy; however, she developed massive right pleural effusion with superior vena cava syndrome and finally succumbed to the disease, three months later.
Conclusion: Adenocarcinoma is rarely found in MCT. This is the first case of ovarian adenocarcinoma arising in MCT with secondary vaginal involvement, presenting as postcoital vaginal bleeding.

Keywords: Adenocarcinoma, Malignant transformation, Mature cystic teratoma, Vaginal involvement, Ovary