Male Extragonadal Germ Cell Tumors of the Adult

Male extragonadal germ cell tumors (EGCTs) are characterized by a malignant transformation of germ cells without the presence of a gonadal primary tumor. EGCTs represent up to 5% of all germ cell tumors (GCTs) with an incidence around 1/1,000,000. It is assumed that EGCTs either derive from a malignant transformation of germ cells that were misdirected during embryogenesis, or from germ cells that have spread throughout the body during embryogenesis to fulfil different roles in immunological processes or distinct organ functions. EGCTs are mainly localized along the median axis, especially in the mediastinum and in the retroperitoneum. Regarding histology, they have the same subtypes as gonadal GCTs (seminomas and non-seminomas). EGCTs are normally diagnosed in advanced stages due to tumor-associated symptoms or as incidental finding during routine diagnostic or therapeutic procedures. An integral part of EGCT treatment is cisplatinum-based chemotherapy: residual tumor resection is only indicated for non-seminomatous EGCTs. The prognosis of malignant retroperitoneal EGCTs depends on tumor localization and histology. The 5-year overall survival ranges from 40% to 90% and is more favorable for retroperitoneal or seminomatous tumors than for mediastinal non-seminomatous tumors. Mature teratomas of mediastinal EGCTs are benign and are only treated by surgical resection.