Extragonadal germ cell tumors are made up of cells that form during the early development of a fetus (unborn baby). In a growing fetus, germ cells typically move from a site near the middle of the body to the ovaries or testes (gonads). There they develop into eggs in females and sperm in males.
When cells that are meant to form sperm or eggs travel to other parts of the body instead, they can form tumors outside the gonads. That's why they are often called extragonadal germ cell tumors. They usually begin in the lungs, the lower back, the back of the abdomen, or the middle of the brain, near the pea-sized pineal gland.
Extragonadal germ cell tumors (EGCTs) are rare. EGCTs are classified as seminomas or nonseminomas (of which there are several subtypes). In children, EGCTs affect boys and girls equally. But in adults, the vast majority of these tumors affect men.
The cells of each type of tumor look different under a microscope. Also, each has a different prognosis and treatment. Seminomas tend to be very responsive to radiation therapy, making that the mainstay for treatment. Chemotherapy is often used treat nonseminomas, but it may be used to treat seminomas as well.
This article will focus on seminomas and nonseminomas.