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.

Epidemiology
Although 20% to 25% of all benign and malignant ovarian neoplasms are of germ cell origin, only about 3% of these tumors are malignant. Germ cell malignancies account for less than 5% of all ovarian cancers in Western countries but they represent up to 15% of ovarian cancers in Asian and black societies, where epithelial ovarian cancers are much less common.

In the first 2 decades of life, almost 70% of ovarian tumors are of germ cell origin, and one third of these are malignant. Germ cell tumors account for two thirds of the ovarian malignancies in this age group. Germ cell cancers also are seen in the third decade, but thereafter become quite rare.

Clinical Features
The most common symptom in young patients with a germ cell tumor of the ovary is a pelvic fullness, urinary frequency, or dysuria. Rectal pressure, menstrual irregularities in postmenarchal patients, and lower abdominal pain or pressure may be present. Some young patients may misinterpret the early symptoms of a neoplasm as those of pregnancy, and this can lead to a further delay in the diagnosis of the cancer. Acute symptoms associated with the torsion or rupture of the adnexa can develop. These symptoms may be confused with acute appendicitis. In more advanced cases, ascites may develop and the patient can present with extensive abdominal distension.

In patients with a palpable adnexal mass, the evaluation should proceed expeditiously. Some patients with germ cell tumors will be premenarchal and may require examination under anesthesia. If the lesions are principally solid or a combination of solid and cystic, as might be noted on an ultrasonographic evaluation, a neoplasm is probable and a malignancy is possible. The rest of the physical examination should search for signs of ascites, pleural effusion, and organomegaly.