Imaging studies and blood tests are used to detect (find) and diagnose childhood extracranial germ cell tumors. The following tests and procedures may be used:         -   Physical exam and history : An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. The testicles may be checked for lumps, swelling, or pain. A history of the patient's health habits and past illnesses and treatments will also be taken.     -   Serum tumor marker test : A procedure in which a sample of blood is checked to measure the amounts of certain substances released into the blood by organs, tissues, or tumor cells in the body. Certain substances are linked to specific types of cancer when found in increased levels in the blood. These are called tumor markers.  Most malignant germ cell tumors release tumor markers. The following tumor markers are used to detect extracranial germ cell tumors:                - Alpha-fetoprotein (AFP).      - Beta-human chorionic gonadotropin (-hCG).          For testicular germ cell tumors, blood levels of the tumor markers help show if the tumor is a seminoma or nonseminoma.    -   Blood chemistry studies : A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by organs and tissues in the body. An unusual (higher or lower than normal) amount of a substance can be a sign of disease.    -   Chest x-ray : An x-ray of the organs and bones inside the chest. An x-ray is a type of energy beam that can go through the body and onto film, making a picture of areas inside the body.    -   CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.    -   MRI (magnetic resonance imaging): A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body. This procedure is also called nuclear magnetic resonance imaging (NMRI).    -   Ultrasound exam: A procedure in which high-energy sound waves (ultrasound) are bounced off internal tissues or organs and make echoes. The echoes form a picture of body tissues called a sonogram. The picture can be printed to be looked at later.    -   Biopsy : The removal of cells or tissues so they can be viewed under a microscope by a pathologist to check for signs of cancer. In some cases, the tumor is removed during surgery and then a biopsy is done. The following tests may be done on the sample of tissue that is removed:               -  Cytogenetic analysis : A laboratory test in which cells in a sample of tissue are viewed under a microscope to look for certain changes in the chromosomes.       -  Immunohistochemistry : A test that uses antibodies to check for certain antigens in a sample of tissue. The antibody is usually linked to a radioactive substance or a dye that causes the tissue to light up under a microscope. This type of test may be used to tell the difference between different types of cancer.