Extragonadal germ cell tumors.

Germ cell cancer is the most common malignancy in men aged 15–35 years; 5% of the malignant germ cell tumors are of extragonadal origin [1]. An extragonadal germ cell tumor (EGGCT) is by definition a germ cell neoplasm displaying one of the histologies associated with gonadal origin, but located outside of the gonads. This specific clinical entity was first described in the 19th century [2, 3]. Histological, serological and cytogenetic characteristics of EGGCTs are similar to those of primary testicular germ cell tumors, but major differences in clinical behavior suggest that gonadal and extragonadal tumors are biologically different (Table 1). In particular, this is true of primary mediastinal EGGCTs and tumors originating in the sacrococcygeal or pineal region; in contrast, tumors arising in the retroperitoneum are more often associated with premalignant lesions in one of the testes and behave clinically in a manner very similar to that of the primary testis counterpart. Also male patients with carcinoma of unknown primary (CUP syndrome) with undifferentiated histology and typical germ cell tumor serum markers, as well as presentation in the midline structures, belong to the group of EGGCT. However, in practice it may be difficult to distinguish extragonadal tumors from metastatic tumors where the primary testis lesion has regressed, e.g. in some cases a scar is found in the testis probably representing a ‘burn-out’ or ‘autoinfarcted’ primary [4]. Furthermore, it is unclear whether the presence of a carcinoma in situ or intraepithelial germ cell neoplasia represents a primary tumor lesion resulting in metastatic deposits e.g. in the mediastinum or retroperitoneum, or whether this testicular lesion represents a general premalignant or malignant change of germ cells at any location distributed in the body, leading to an extragonadal malignant tumor.