| Summary: | Abstract Background Ovarian mature cystic teratomas comprise tissues derived from all three germ layers. In rare incidences, malignant tumors may arise from ovarian mature cystic teratoma, which occurs in 0.2–1.8% of cases. A variety of tumors can arise within mature cystic teratoma, among which malignant melanoma is exceedingly rare. Case presentation A 42-year-old woman presented with abdominal pain. Transvaginal ultrasonography showed mixed echogenic cystic masses in both ovaries. Her serum cancer antigen (CA19–9) level was elevated at 29,770 U/ml. Surgical excision was performed. Histologic examination showed infiltrating nests of pleomorphic cells with prominent nucleoli and black pigments in the background of a mature cystic teratoma. These pleomorphic cells showed strong immunoreactivity for Melan-A and HMB-45. The patient was re-evaluated and the possibility of a melanoma at any other site was ruled out. Based on these findings, we concluded that the malignant melanoma originated from the ovarian mature cystic teratoma. Conclusion We report a rare case of primary malignant melanoma derived from an ovarian mature cystic teratoma.
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