How would you approach risk-stratification/staging of a extra-gonadal germ cell tumor with both mediastinal and retroperitoneal lymphadenopathy?   

Actually there is zero chance a primary mediastinal germ cell tumor would ever have retrograde adenopathy to the RPLN's. Thus this is a primary retroperitoneal germ cell tumor. Assuming no non-pulm visceral mets and markers at good risk level, would treat with BEP x 3. You did not mention patho...