A rare case of multiple malignant tumors (poorly differentiated squamous cell carcinoma and high grade osteosarcoma) arising in an ovarian dermoid cyst of a 55 year old female is reported. To the best of our knowledge, this is the first well documented example of such an unusual combination of tumors arising in a dermoid cyst. The osteosarcoma and squamous cell carcinoma appear to arise in the background of benign teratomatous environment of a dermoid cyst rather than from "pure" mixed mesodermal tumors of the ovary. The tumors did not appear to have well demarcated boundaries with a junction or close intermingling of both cell types, features less favorable for collision tumor or carcinosarcoma. Despite extensive surgery with negative surgical margins and combination chemotherapy, the patient had recurrence of the tumor within four months and she died secondary to septicemia to chemotherapy and bilateral pulmonary emboli shortly after.
Keywords: Malignant dermoid; osteosarcoma; squamous cell carcinoma; teratoma.