Abstract
Ovarian mature cystic teratomas comprise tissue derived from all three germ layers and constitute 10-20% of all ovarian neoplasms. Malignant transformation of mature cystic teratomas (MCT) is very rare with an incidence of 0.17-2%. The most frequently reported malignancies include squamous cell carcinoma and adenocarcinoma. Herein, we describe a case of a 56-year-old female who presented with abdominal pain and underwent total abdominal hysterectomy with bilateral oophorectomy and omentectomy for a ruptured dermoid cyst. Histological examination showed nests of pleomorphic cells with prominent nucleoli and melanin pigment in the background of a mature cystic teratoma. These cells showed immunoreactivity for Melan-A and HMB-45, thus confirming the diagnosis of malignant transformation of a mature cystic teratoma to a malignant melanoma.