Endodermal Sinus (Yolk Sac) Tumor

This tumor is rare but is the second most common malignant tumor of germ cell origin. It is thought to be derived from differentiation of malignant germ cells along the extra-embryonic yolk sac lineage (see Fig. 22-42). Similar to the normal yolk sac, the tumor is rich in α-fetoprotein and α1-antitrypsin. Its characteristic histologic feature is a glomerulus-like structure composed of a central blood vessel enveloped by germ cells within a space lined by germ cells (Schiller-Duval body) (Fig. 22-47). Conspicuous intracellular and extracellular hyaline droplets are present in all tumors, and some of these stain for α-fetoprotein by immunoperoxidase techniques.

Most patients are children or young women presenting with abdominal pain and a rapidly developing pelvic mass. The tumors usually appear to involve a single ovary but grow rapidly and aggressively. These tumors were once almost uniformly fatal within 2 years of diagnosis, but combination chemotherapy has measurably improved the outcome.

Choriocarcinoma

More commonly of placental origin, the choriocarcinoma, like the endodermal sinus tumor, is an example of extra-embryonic differentiation of malignant germ cells. It is generally held that a germ cell origin can be confirmed only in the prepubertal girl, because after this age an origin from an ovarian ectopic pregnancy cannot be excluded.

Most ovarian choriocarcinomas exist in combination with other germ cell tumors, and pure choriocarcinomas are extremely rare. They are histologically identical to the more common placental lesions, described later. The ovarian primaries are aggressive tumors that generally have metastasized widely through the bloodstream to the lungs, liver, bone, and other viscera by the time of diagnosis. Like all choriocarcinomas they elaborate high levels of chorionic gonadotropins, which is sometimes helpful in establishing the diagnosis or detecting recurrences. In contrast to choriocarcinomas arising in placental tissue, those arising in the ovary are generally unresponsive to chemotherapy and are often fatal.

Other Germ Cell Tumors

These include (1) embryonal carcinoma, another highly malignant tumor of primitive embryonal elements, histologically similar to tumors arising in the testes (Chapter 21)75; (2) polyembryoma, a malignant tumor containing so-called embryoid bodies; and (3) mixed germ cell tumors containing various combinations of dysgerminoma, teratoma, endodermal sinus tumor, and choriocarcinoma.

SEX CORD-STROMAL TUMORS

These ovarian neoplasms are derived from the ovarian stroma, which in turn is derived from the sex cords of the embryonic gonad. Because the undifferentiated gonadal mesenchyme eventually produces structures of specific cell type in both male (Sertoli and Leydig) and female (granulosa and theca) gonads, tumors resembling all of these cell types can be identified in the ovary.102 Moreover, because some of these cells normally secrete estrogens (granulosa and theca cells) or androgens (Leydig cells), their corresponding tumors may be either feminizing (granulosa-theca cell tumors) or masculinizing (Leydig cell tumors).