Germ cell tumors (GCTs) are abnormal growths that develop from germ cells. The name “germ cell” does not refer to infections or other germs, but is rather related to the word “germinate” because they are reproductive cells.
During normal fetal development, germ cells migrate into place in the reproductive organs to become either eggs or sperm. Germ cell tumors, therefore, mostly occur in the gonads – the ovaries or testicles – and cause ovarian or testicular cancer. In some rare instances, however, germ cells end up in the wrong place in the body, known as extragonadal germ cells. When germ cells are misplaced into the developing brain, they too may develop into tumors. Primary central nervous system (CNS) germ cell tumors are very rare, but when they do occur they are frequently malignant. They are mostly found in children and young adults between the ages of 10 and 30.
A germ cell tumor may be either a pure germinoma, a non-germinomatous GCT tumor (NGGCT), or a mixed germ cell tumor. There is a subtype of germinoma that is referred to a secretory germinoma or germinoma with syncytiotrophoblastic features, or intermediate risk germinoma. NGGCT are further subdivided into embryonal carcinoma, a yolk sac tumor, or a teratoma (mature or immature). Treatment for a germ cell tumor can be very variable and is dependent on this classification.
What Causes a Germ Cell Tumor?
As with most tumors, the factors that can trigger the formation of a germ cell tumor are not well understood. Some genetic conditions affecting sex chromosomes seem to increase the likelihood of developing a germ cell tumor, and a family history may also increase the risk. There does exist a strong ethnic predisposition in individuals of Asian descent. But many germ cell tumors in the brain arise spontaneously, meaning there is no known cause. They may simply be a case of the extremely intricate process of human development going awry during fetal development.
Reviewed by Mark M. Souweidane, MD
Last reviewed/last updated: December 2020
Illustrations by Thom Graves CMI