Angiosarcoma masquerading as embryonal carcinoma in the metastasis from a mature testicular teratoma

Sarcoma can arise within a germ cell tumor (GCT) from a malignant transformation of teratomatous elements or as late sequelae to radiation therapy. Angiosarcoma as a malignant component in testicular GCTs has rarely been reported and is often misdiagnosed as embryonal carcinoma. We report the case of a 23-year-old man with mature teratoma of the testis and retroperitoneal metastasis exhibiting components of mature teratoma intermingled with high-grade angiosarcoma. It is important to recognize the presence of a high-grade sarcomatous component within a GCT because of its aggressive clinical behavior and different response to therapy.