Primary germ cell tumors of the mediastinum: a review

Primary mediastinal germ cell tumors (M-GCT) are unusual tumors that bear similar histopathological features to those occurring in other anatomical areas such as the gonads. Due to this similarity, the mere existence of these tumors in the past was questioned. However, today, there is no doubt that these tumors just like those in the gonads, occur in the mediastinal compartment or along the midline. Nevertheless, it is important to highlight that because all of these tumors share similar histopathological features, it is always prudent to rule out the possibility of metastatic disease to the mediastinum. The nomenclature that is followed for M-GCT is similar to that applied to testicular tumors with a few semantic differences. However, it is important to recognize that the spectrum of M-GCT that has been described in the literature is much more limited than the one reported in the gonads. In addition, it is also important to recognize that whenever possible, staging of these tumors is essential in order to predict clinical outcome. The emphasis in this review will be on histopathological diagnosis with the application of ancillary tools, including immunohistochemistry, and also the use of proper nomenclature and staging. A discussion of possible mimickers that may play a role in the differential diagnosis of these tumors will also be presented.