Mediastinal germ cell tumors

Mediastinal germ cell tumors (GCTs) are rare and encompass less than one fifth of all mediastinal neoplasms in adults and children. These tumors predominantly occur in men. Most mediastinal GCTs are located in the anterior mediastinum. The vast majority of mediastinal GCTs are considered primary mediastinal tumors; however, a metastatic process from the gonads should always be excluded. Although these tumors morphologically resemble their gonadal counterparts, there are differences in prognosis. For instance, in contrast to immature teratomas in the gonads, immature teratomas in the mediastinum might behave in an aggressive fashion. Klinefelter syndrome is the only abnormality that has been associated with mediastinal GCT. Furthermore, the differential diagnostic considerations in the mediastinum differ from GCT elsewhere. Expression of certain GCT markers by its mimickers in the mediastinum might pose a potential pitfall. This chapter will focus on features of mediastinal GCT that might differ from their gonadal counterpart including imaging, immunophenotype, cytogenetic and molecular characteristics, and prognosis. Important differential diagnoses that should be considered before establishing a diagnosis of primary mediastinal GCT will also be discussed.