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A germ cell tumor is a cancer that develops from cells in the reproductive system called germ cells. In men, germ cells are responsible for producing sperm. Most germ cell tumors in teenage boys and men start in one of the testicles. There are two different categories of germ cell tumors: seminoma and non-seminoma. Generally, seminomas grow and spread more slowly than non-seminomas, but both types of tumors should be treated quickly.
A germ cell tumor can also develop in other parts of the body, such as the retroperitoneum (the back of the abdomen near the spine), the mediastinum (the central portion of the chest between the lungs), the lower spine, and very rarely, the pineal gland (a small gland in the brain).
During diagnosis of a germ cell tumor, a sample of blood may be collected to test for levels of serum tumor markers, which are substances produced by a cancer that are found at abnormally high levels in the blood of a person with that cancer. High levels of any one of three tumor markers, called alpha-fetoprotein (AFP), beta human chorionic gonadotropin (hCG), and lactate dehydrogenase (LDH), may indicate a germ cell tumor. High AFP levels can also help identify the type of germ cell tumor, by showing whether it is a pure seminoma or mixed with non-seminoma, since AFP is not made by seminomas. However, hCG and/or LDH can be higher if a man has a seminoma, non-seminoma, or mixed tumor. If markers are elevated at diagnosis, changes in their levels can tell your doctor whether the tumor is responding to treatment.