Germ Cell Malignancies

Germ cell tumors are derived from the primordial germ cells of the ovary. Whereas malignant germ cell tumors can arise in extragonadal sites, such as the mediastinum and the retroperitoneum, the majority of germ cell tumors arise in the gonad from the undifferentiated germ cells. The variation in the sites of these cancers is explained by the embryonic migration of the germ cells from the caudal part of the yolk sac to the dorsal mesentery, prior to their incorporation into the sex cords of the developing gonads.

Classification
A histologic classification of ovarian germ cell tumors is presented in Table 118-9. α-fetoprotein (AFP) and human chorionic gonadotropin (hCG) are both secreted by some germ cell malignancies and, therefore, the presence of circulating hormones can be clinically useful in the diagnosis of a pelvic mass and in monitoring the course of a patient after surgery. α-1-antitrypsin (AAT) can be detected rarely in association with germ cell tumors. By correlating the histologic and immunohistologic identification of these substances in tumors, a classification of germ cell tumors can be made. In this classification, embryonal carcinoma, which is composed of undifferentiated cells, synthesizes both hCG and AFP, and this tumor is the progenitor of several other germ cell malignancies. More differentiated germ cell tumors, such as the endodermal sinus tumor, which secretes AFP, and the choriocarcinoma, which secretes hCG, are derived from the extraembryonic tissues, whereas the immature teratomas are derived from the embryonic cells that have lost the ability to secrete these substances. Pure germinomas do not secrete these markers.