FDG-PET evaluation of retroperitoneal metastases of testicular cancer before and after chemotherapy.

We describe a patient whose primary tumor was a testicular teratocarcinoma predominantly composed of embryonal carcinoma. Before chemotherapy, the retroperitoneal metastases demonstrated heterogeneous, increased glucose metabolism as measured by 2-[18F]fluoro-2-deoxy-D-glucose and PET (FDG-PET). After chemotherapy, FDG uptake was reduced to normal values despite increased tumor volume. Histology revealed a pure mature teratoma. This observation suggests that further studies are needed to determine whether tumor differentiation of testicular teratocarcinoma metastases can be assessed by measuring glucose metabolism.