Thymoma and thymic carcinoma arising in a thymolipoma: report of a unique case.

Thymic carcinoma arising within a thymolipoma has not been reported previously. The authors present a unique case of thymoma and undifferentiated thymic carcinoma arising within a thymolipoma in a 36-year-old woman. The bulk of the resected mass was composed of benign fatty tissue admixed with foci of unremarkable thymic tissue; however, it also harbored a central solid mass showing undifferentiated thymic carcinoma associated with a type B2 thymoma. The carcinoma cells were positive for cytokeratin AE1/AE3, cytokeratin 19, and cytokeratin 8/18. They were negative for vimentin, cytokeratin 7, cytokeratin 20, CD5, epithelial membrane antigen, CD30, placental alkaline phosphatase, carcinoembryonic antigen, CD99, leukocyte common antigen, Epstein-Barr virus, inhibin alpha, and protein gene product 9.5. Rare tumor cells showed positive staining for chromogranin and synaptophysin.