What are Germ Cell Tumors?

Germ cell tumors (GCTs) are a neoplasm, or an abnormal growth of cells resulting in a mass of tissue, that are derived from the germ cells, the precursors of the gametes or sex cells, namely eggs and sperm. GCTs most often arise in the ovaries or testes, known collectively as the gonads, but they may also occur during embryonic development, resulting in a birth defect. This latter type of tumor can affect the head, neck, chest, or pelvis. Like other tumors, germ cell tumors are treated with either chemotherapy if malignant, surgery, or a combination thereof.

Germ cell tumors are responsible for about one to three percent of ovarian cancers, and about 95% of testicular cancers. About 30% of ovarian tumors are germ cell tumors, but most of these are benign teratomas rather than malignant cancerous tumors. Most tumors outside of the gonads are also teratomas.

Teratomas are encapsulated tumors characterized by having components of the three germ layers, the endoderm, mesoderm, and ectoderm, which normally arise during the growth of the embryo, and give rise to all mature tissues and organs. Teratomas may include many different types of body tissue, including teeth, bone, hair, and tissues normally found in various organs, like the brain or lungs. Though most are benign, malignant teratomas do exist.

Germ cell tumors are characterized based on their histology, or microscopic anatomy, regardless of their location in the body. They may be germinomatous (GGCT), also called seminomatous (SGCT), or they may be nongerminomatous (NGGCT), also called nonseminomatous (NSGCT). GGCTs are also called germinomas, and are distinguished by being undifferentiated, meaning that the cells have a uniform microscopic appearance that is not associated with any mature tissue type. Germinomas of the ovary are called dysgerminoma, while those of the testis are called seminoma. Germinomas are malignant, and the most common cause of ovarian cancer and the second most common cause of testicular cancer.

NGGCTs come in many varieties. In addition to the teratomas discussed above, they may be embryonal carcinoma, endodermal sinus tumor or yolk sack tumor, choriocarcinoma, polyembryoma, gonadoblastoma, or mixed. Embryonal carcinoma, endodermal sinus tumor, and choriocarcinoma are all malignant. In contrast, endodermal sinus tumor is usually present at birth, and has a very good prognosis. Choriocarcinoma usually affects the placenta of a pregnant woman and can quickly spread to the lungs; it is the most aggressive type of germ cell tumor.

Polyembryoma and gonadoblastoma are relatively rare. Mixed cell tumors are any mixture of the other types discussed, and are always malignant. Some common forms are teratomas mixed with endodermal sinus tumor, and teratocarcinoma, which is a mixture of teratoma with either embryonal carcinoma or choriocarcinoma.