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Glossary - G

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  • G tube

    (... toob)

    A tube inserted through the wall of the abdomen directly into the stomach. It allows air and fluid to leave the stomach and can be used to give drugs and liquids, including liquid food, to the patient. Giving food through a gastrostomy tube is a type of enteral nutrition. Also called PEG tube and percutaneous endoscopic tube.

  • G6PD deficiency

    (… deh-FIH-shun-see)

    An inherited disorder in which a person doesn’t have enough of an enzyme called G6PD that helps red blood cells work the way they should. In G6PD deficiency, the red blood cells break down when the body is exposed to infection, severe stress, or certain drugs, chemicals, or foods. This may lead to a condition called hemolytic anemia. This disorder is most common in African-American men and in men of Middle Eastern or Mediterranean descent. Also called glucose-6-phosphate dehydrogenase deficiency.

  • Gadolinium


    A metal element that is used in magnetic resonance imaging (MRI) and other imaging methods. It is a contrast agent, which helps show abnormal tissue in the body during imaging with a special machine.

  • Gallbladder


    The pear-shaped organ found below the liver. Bile is concentrated and stored in the gallbladder.

  • Gamma globulin

    A protein component of blood plasma containing antibodies effective against certain micro organisms.

  • Gamma ray

    (GA-muh ...)

    A type of high-energy radiation that is different from an x-ray.

  • Gastric


    Having to do with the stomach.

  • Gastric feeding tube

    (GAS-trik FEE-ding toob)

    A tube that is inserted through the nose, down the throat and esophagus, and into the stomach. It can be used to give drugs, liquids, and liquid food, or used to remove substances from the stomach. Giving food through a gastric feeding tube is a type of enteral nutrition. Also called nasogastric tube and NG tube.

  • Gastroenterologist


    A doctor who specializes in diseases of the digestive (gastrointestinal) tract.

  • Gastrointestinal


    Refers to the stomach and intestines. Also called GI.

  • Gastrointestinal stromal tumor

    (GAS-troh-in-TES-tih-nul STROH-mul TOO-mer)

    A type of tumor that usually begins in cells in the wall of the gastrointestinal tract. It can be benign or malignant. Also called GIST.

  • Gastrointestinal tract

    (GAS-troh-in-TES-tih-nul trakt)

    The digestive tract. It consists of those organs and structures that process and prepare food to be used for energy; for example, the stomach, small intestine and large intestine.

  • Gastrostomy tube

    (gas-TROS-toh-mee toob)

    A tube inserted through the wall of the abdomen directly into the stomach. It allows air and fluid to leave the stomach and can be used to give drugs and liquids, including liquid food, to the patient. Giving food through a gastrostomy tube is a type of enteral nutrition. Also called PEG tube and percutaneous endoscopic tube.

  • Gavage


    A way of giving medicines and liquids, including liquid foods, through a small tube placed through the nose or mouth into the stomach or small intestine. Sometimes the tube is placed into the stomach or small intestine through an incision (cut) made on the outside of the abdomen. Gavage may be added to what a person is able to eat and drink, or it may be the only source of nutrition. It is a type of enteral nutrition. Also called tubefeeding.

  • Gene


    A piece of DNA that serves as the instructions to tell the cells of the body how to function. Most cells of the body have 2 copies of each gene, one passed down (inherited) from the mother and one from the father.

  • Gene therapy

    jeen THAYR-uh-pee

    A type of experimental treatment in which foreign genetic material (DNA or RNA) is inserted into a person's cells to prevent or fight disease. Gene therapy is being studied in the treatment of certain types of cancer.

  • General anesthesia

    JEH-neh-rul A-nes-THEE-zhuh

    A temporary loss of feeling and a complete loss of awareness that feels like a very deep sleep. It is caused by special drugs or other substances called anesthetics. General anesthesia keeps patients from feeling pain during surgery or other procedures.

  • Generic


    Official nonbrand names by which medicines are known. Generic names usually refer to the chemical name of the drug.

  • Genetic


    Having to do with genes. Most genes are sequences of DNA that contain information for making specific proteins or molecules of RNA that perform important functions in a cell. The information in genes is passed from parents to children.

  • Genetic counselor

    A specially trained health care professional who helps patients and families understand how genetics and genomics impact their health and development.

  • Genetic predisposition

    An increased chance to develop a certain condition because a change (mutation) is present in one or more genes within the body’s cells.

  • Genetic testing

    (jeh-NEH-tik TES-ting)

    The process of analyzing cells or tissues to look for genetic changes that may be a sign of a disease or condition, such as cancer. These changes may be a sign that a person has an increased risk of developing a specific disease or condition.

  • Genetics


    The study of genes and heredity. Heredity is the passing of genetic information and traits (such as eye color and an increased chance of getting a certain disease) from parents to offspring.

  • Genome

    The entire set of genes. Human cells carry around 20,000 different genes.

  • Genomics

    The study of the entire set of genes and their effects on health and development.

  • Germ


    A bacterium, virus, or other microorganism that can cause infection and disease.

  • Germ cell

    (jerm sel)

    A reproductive cell of the body. Germ cells are egg cells in females and sperm cells in males.

  • Germ cell tumor

    jerm sel TOO-mer

    A type of tumor that begins in the cells that give rise to sperm or eggs. Germ cell tumors can occur almost anywhere in the body and can be either benign or malignant.

  • GIST

    A type of tumor that usually begins in cells in the wall of the gastrointestinal tract. It can be benign or malignant. Also called gastrointestinal stromal tumor.

  • Glands


    Organs that makes one or more substances, such as hormones, digestive juices, sweat, tears, saliva, or milk. Endocrine glands release the substances directly into the bloodstream. Exocrine glands release the substances into a duct or opening to the inside or outside of the body.

  • Glial cells

    GLEE-ul sel

    Any of the cells that hold nerve cells in place and help them work the way they should. The types of glial cells include oligodendrocytes, astrocytes, microglia, and ependymal cells. Also called neuroglia.

  • Glucose


    A type of sugar; the chief source of energy for living organisms.

  • Glycogen storage disease

    (GLY-koh-jen STOR-ij dih-ZEEZ)

    A type of inherited disorder in which there are problems with how a form of glucose (sugar) called glycogen is stored and used in the body. Certain enzymes that help make or break down glycogen are missing or do not work the way they should. This causes abnormal amounts or types of glycogen in the tissues, especially in the liver and in muscle tissue. There are many types of glycogen storage disease, which can cause problems in different parts of the body, including the liver, muscles, kidneys, and heart. Also called GSD.

  • Gonadotropin-releasing hormone

    (goh-NA-doh-TROH-pin-reh-LEE-sing HOR-mone)

    A hormone made by a part of the brain called the hypothalamus. Gonadotropin-releasing hormone causes the pituitary gland in the brain to make and secrete the hormones luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In men, these hormones cause the testicles to make testosterone. In women, they cause the ovaries to make estrogen and progesterone. Also called GnRH, LH-RH, LHRH, and luteinizing hormone-releasing hormone.

  • Gout


    A condition marked by increased levels of uric acid in the blood, joints, and tissue. The buildup of uric acid in the joints and tissues causes arthritis and inflammation.

  • Grade


    In cancer, a description of a tumor based on how abnormal the cancer cells and tissue look under a microscope and how quickly the cancer cells are likely to grow and spread. Low-grade cancer cells look more like normal cells and tend to grow and spread more slowly than high-grade cancer cells. Grading systems are different for each type of cancer. They are used to help plan treatment and determine prognosis. Also called histologic grade and tumor grade.

  • Grading


    A system for classifying cancer cells in terms of how abnormal they appear when examined under a microscope. The objective of a grading system is to provide information about the probable growth rate of the tumor and its tendency to spread. The systems used to grade tumors vary with each type of cancer. Grading plays a role in treatment decisions.

  • Graft


    Healthy skin, bone, or other tissue taken from one part of the body and used to replace diseased or injured tissue removed from another part of the body.

  • Graft versus host disease

    The condition that results when the immune cells of a transplant (usually of bone marrow) from a donor attack the tissues of the person receiving the transplant. A reaction of engrafted tissue against your own tissue.

  • Graft-versus-tumor


    An immune response to a person's tumor cells by immune cells present in a donor's transplanted tissue, such as bone marrow or peripheral blood.

  • Granular cell tumor

    (GRAN-yoo-lur sel TOO-mer)

    A rare type of soft tissue tumor that usually begins in Schwann cells (cells that hold nerve cells in place). It can occur anywhere in the body, but it usually occurs in or under the skin of the head and neck (especially the mouth or tongue). It may also occur in the chest, breast, esophagus, stomach, or other internal organ. Most granular cell tumors are benign (not cancer), but some may be malignant (cancer) and spread quickly to nearby tissue. They usually occur in middle-aged adults. Also called Abrikossoff tumor.

  • Granulocytes

    White blood cells that help to protect you against bacterial infection; also called ""polys"", ""segs"", or neutrophils.

  • Grief


    The normal response to a major loss, such as the death of a loved one. Grief may also be felt by a person with a serious, long-term illness or with a terminal illness. It may include feelings of great sadness, anger, guilt, and despair. Physical problems, such as not being able to sleep and changes in appetite, may also be part of grief.

  • Groin


    The area of your body where the legs join the abdomen.

  • Growth and development and milestones

    (grothe ... dee-VEH-lup-MENT MILE-stones)

    Goals for the expected sizes of infants and children and activities they should be able to do at specific ages, such as sit, stand, play, speak, think, and interact with others.

  • Growth factors

    grothe FAK-ter

    A naturally occurring protein that causes cells to grow and divide. Too much growth factor production by some cancer cells helps them grow quickly. Other growth factors help normal cells recover from side effects of chemotherapy.

  • Guided imagery

    (GY-ded IH-muh-jree)

    A technique in which a person focuses on positive images in his or her mind. It can help people reach a relaxed, focused state and help reduce stress and give a sense of well-being. Also called imagery.

  • Gy

    The new international system (SI) unit of radiation dose, expressed as absorbed energy per unit mass of tissue. The SI unit "gray" has replaced the older "rad" designation. 1 Gy = 1 Joule/kilogram = 100 rad. Gray can be used for any type of radiation (e.g., alpha, beta, neutron, gamma), but it does not describe the biological effects of different radiations. Biological effects of radiation are measured in units of "sievert" (or the older designation "rem"). Sievert is calculated as follows: gray multiplied by the "radiation weighting factor" (also known as the "quality factor") associated with a specific type of radiation.