A case of chondrosarcoma developing in a recurrent retroperitoneal mass after chemotherapy for testicular germ cell tumor.

Teratomas with malignant transformation occur in a small proportion of patients with metastatic germ cell tumors treated with platinum-based chemotherapy. Chondrosarcoma has rarely been reported as a component of the second non-germ cell malignancy. We report the case of a 37-year-old man who developed a chondrosarcoma in a recurrent retroperitoneal mass after chemotherapy for testicular germ cell tumor. Malignant transformation of the retroperitoneal teratomatous mass occurred in the absence of any symptoms or clinical signs, elevation in serum tumor markers, or the presence of atypical elements in previously resected specimens, suggesting the need for close radiographic follow-up of these patients.