31. A malignant melanoma arising in a mature cystic teratoma

Abstract

Introduction and background Mature cystic teratoma is the most common ovarian germ cell neoplasm and childhood ovarian tumour. Malignant change in a mature cystic teratoma is rare. Most common malignancy arising in a teratoma is squamous cell carcinoma. Only 32 cases of a malignant melanoma arising in a mature cystic teratoma have been reported in the world literature to date. Clinical presentation A 37-year-old female presented with a recent history of lower back pain. X-ray showed a tooth like structure in the right ovary. Ultrasound revealed features of a dermoid cyst. She underwent surgical excision of the dermoid cyst. Methods, Macroscopic and microscopic features: Macroscopy A 50 mm cyst, containing greasy yellow material and hair shafts. Two nodules noted within the cyst wall, a 35×26×26 mm fatty nodule centred by a misshapen tooth and an intramural 16×10mm pigmented nodule. Microscopy A mixture of skin and skin appendages, conjunctival lining, fibroadipose tissue and mature neural elements. The pigmented nodule consisted of a whorled proliferation of melanocytes exhibiting pronounced cellular pigmentation and moderate cyto-logical atypia. The final diagnosis was malignant melanoma arising in a mature cystic teratoma confirmed by S100, HMB45, Melan A, Perl’s stain, Schmorl’s stains. Peritoneal washings cytology no malignant cells. Discussion This is a rare change in a relatively common benign entity that can be easily overlooked. It emphasises how distinction between a benign or borderline melanocytic proliferation and a malignant melanoma can be challenging. The importance of adequate sampling and use of immunohistochemistry techniques is revealed. Moreover, previous data supports a role for chemotherapy. This case has had the best outcome reported in the literature despite no additional chemotherapy.