This is a medical question of type : information 
 What is (are) Childhood Extracranial Germ Cell Tumors ? 
 Key Points
                    - Childhood extracranial germ cell tumors form from germ cells in parts of the body other than the brain.    - Childhood extracranial germ cell tumors may be benign or malignant.    - There are three types of extracranial germ cell tumors.         - Mature Teratomas      - Immature Teratomas      - Malignant Germ Cell Tumors        - Childhood extracranial germ cell tumors are grouped as gonadal or extragonadal.          - Gonadal Germ Cell Tumors     - Extragonadal Extracranial Germ Cell Tumors        - The cause of most childhood extracranial germ cell tumors is unknown.    - Having certain inherited disorders can increase the risk of an extracranial germ cell tumor.    - Signs of childhood extracranial germ cell tumors depend on the type of tumor and where it is in the body.    - Imaging studies and blood tests are used to detect (find) and diagnose childhood extracranial germ cell tumors.    - Certain factors affect prognosis (chance of recovery) and treatment options.
                
                
                    Childhood extracranial germ cell tumors form from germ cells in parts of the body other than the brain.
                    A germ cell is a type of cell that forms as a fetus (unborn baby) develops. These cells later become sperm in the testicles or eggs in the ovaries. Sometimes while the fetus is forming, germ cells travel to parts of the body where they should not be and grow into a germ cell tumor. The tumor may form before or after birth.   This summary is about germ cell tumors that form in parts of the body that are extracranial (outside the brain). Extracranial germ cell tumors usually form in the following areas of the body:          - Testicles.    - Ovaries.    -  Sacrum or coccyx (bottom part of the spine).    - Retroperitoneum (the back wall of the abdomen).    -  Mediastinum (area between the lungs).               Extracranial germ cell tumors are most common in adolescents 15 to 19 years of age.   See the PDQ summary on Childhood Central Nervous System Germ Cell Tumors Treatment for information on intracranial (inside the brain) germ cell tumors.
                
                
                    Childhood extracranial germ cell tumors may be benign or malignant.
                    Extracranial germ cell tumors may be benign (noncancer) or malignant (cancer).
                
                
                    There are three types of extracranial germ cell tumors.
                    Extracranial germ cell tumors are grouped into mature teratomas, immature teratomas, and malignant germ cell tumors:      Mature Teratomas     Mature teratomas are the most common type of extracranial germ cell tumor. Mature teratomas are benign tumors and not likely to become cancer. They usually occur in the sacrum or coccyx (bottom part of the spine) in newborns or in the ovaries of girls at the start of puberty. The cells of mature teratomas look almost like normal cells under a microscope. Some mature teratomas release enzymes or hormones that cause signs and symptoms of disease.       Immature Teratomas     Immature teratomas also usually occur in the sacrum or coccyx (bottom part of the spine) in newborns or the ovaries of girls at the start of puberty. Immature teratomas have cells that look very different from normal cells under a microscope. Immature teratomas may be cancer. They often have several different types of tissue in them, such as hair, muscle, and bone. Some immature teratomas release enzymes or hormones that cause signs and symptoms of disease.       Malignant Germ Cell Tumors     Malignant germ cell tumors are cancer. There are two main types of malignant germ cell tumors:            - Germinomas: Tumors that make a hormone called beta-human chorionic gonadotropin (-hCG). There are three types of germinomas.                  -  Dysgerminomas form in the ovary in girls.       -  Seminomas form in the testicle in boys.       - Germinomas form in areas of the body that are not the ovary or testicle.                - Nongerminomas: There are four types of nongerminomas.                  - Yolk sac tumors make a hormone called alpha-fetoprotein (AFP). They can form in the ovary, testicle, or other areas of the body.       -  Choriocarcinomas make a hormone called beta-human chorionic gonadotropin (-hCG). They can form in the ovary, testicle, or other areas of the body.       -  Embryonal carcinomas may make a hormone called -hCG and/or a hormone called AFP. They can form in the testicle or other parts of the body, but not in the ovary.       - Mixed germ cell tumors are made up of both malignant germ cell tumor and teratoma. They can form in the ovary, testicle, or other areas of the body.
                
                
                    Childhood extracranial germ cell tumors are grouped as gonadal or extragonadal.
                    Malignant extracranial germ cell tumors are gonadal or extragonadal.     Gonadal Germ Cell Tumors    Gonadal germ cell tumors form in the testicles in boys or ovaries in girls.          Testicular Germ Cell Tumors        Testicular germ cell tumors are divided into two main types, seminoma and nonseminoma.               - Seminomas make a hormone called beta-human chorionic gonadotropin (-hCG).      - Nonseminomas are usually large and cause signs or symptoms. They tend to grow and spread more quickly than seminomas.              Testicular germ cell tumors usually occur before the age of 4 years or in adolescents and young adults. Testicular germ cell tumors in adolescents and young adults are different from those that form in early childhood.     Boys older than 14 years with testicular germ cell tumors are treated in pediatric cancer centers, but the treatment is much like the treatment used in adults. (See the PDQ summary on Testicular Cancer Treatment for more information.)             Ovarian Germ Cell Tumors        Ovarian germ cell tumors are more common in adolescent girls and young women. Most ovarian germ cell tumors are benign teratomas. Sometimes immature teratomas, dysgerminomas, yolk sac tumors, and mixed germ cell tumors (cancer) occur. (See the PDQ summary on Ovarian Germ Cell Tumors Treatment for more information.)          Extragonadal Extracranial Germ Cell Tumors    Extragonadal extracranial germ cell tumors form in areas other than the brain, testicles, or ovaries.    Most extragonadal extracranial germ cell tumors form along the midline of the body. This includes the following:             - Sacrum (the large, triangle-shaped bone in the lower spine that forms part of the pelvis).     -  Coccyx (the small bone at the bottom of the spine, also called the tailbone).     -  Mediastinum (the area between the lungs).     -  Back of the abdomen.     -  Neck.           In younger children, extragonadal extracranial germ cell tumors usually occur at birth or in early childhood. Most of these tumors are teratomas in the sacrum or coccyx.    In older children, adolescents, and young adults, extragonadal extracranial germ cell tumors are often in the mediastinum.