A germ cell is a type of cell that forms as a fetus develops. These cells later become sperm in the testicles or eggs in the ovaries. Sometimes, germ cells may develop into a germ cell tumor in other parts of the body, either before or after birth.

An extracranial germ cell tumor is a germ cell tumor that forms in parts of the body other than the brain, such as the gonads (testicles and ovaries), chest, abdomen, or tailbone. Extracranial germ cell tumors are most common in teenagers 15 to 19 years of age.

There are three types of extracranial germ cell tumors. The most common type is mature teratoma, a benign tumor that is not likely to become cancer. Other types are immature teratomas (which may become cancer) and malignant germ cell tumors (cancer).

Extracranial germ cell tumors in children, especially ovarian germ cell tumors or testicular cancer, can usually be cured.