G-CSF: Granulocyte colony-stimulating factor. A substance that stimulates the production of neutrophils, a type of white blood cell. Also called filgrastim.

Gadolinium texaphyrin: A substance that makes tumor cells more sensitive to radiation; it can also enhance tumor images using magnetic resonance imaging (MRI). Gadolinium texaphyrin belongs to the family of drugs called metalloporphyrin complexes.

Gallbladder (GAWL-blad-er): The pear-shaped organ that sits below the liver. Bile is concentrated and stored in the gallbladder.

Gallium nitrate: A drug that lowers blood calcium. Used as treatment for hypercalcemia (too much calcium in the blood) and for cancer that has spread to the bone (bone metastases).

Gamma irradiation: A type of radiation therapy that uses gamma radiation. Gamma radiation is a type of high-energy radiation that is different from x-rays.

Gamma knife: Radiation therapy in which high-energy rays are aimed at a tumor from many angles angles in a single treatment session.

Ganciclovir: An antiviral agent used to prevent or treat cytomegalovirus infections that may occur when the body's immune system is suppressed. In gene therapy, ganciclovir is used with an altered herpes simplex virus-1 gene to kill advanced melanoma cells and brain tumor cells.

Gastrectomy (gas-TREK-toe-mee): An operation to remove all or part of the stomach.

Gastric (GAS-trik): Having to do with the stomach.

Gastric atrophy (GAS-trik AT-ro-fee): A condition in which the stomach muscles shrink and become weak. The digestive (peptic) glands may also shrink, resulting in a lack of digestive juices.

Gastrinoma (gas-tri-NO-ma): A tumor that causes over-production of gastric acid. It usually occurs in the islet cells of the pancreas, but may also occur in the esophagus, stomach, spleen, or lymph nodes.

Gastroenterologist (GAS-tro-en-ter-AHL-o-jist): A doctor who specializes in diagnosing and treating disorders of the digestive system.

Gastrointestinal (GAS-tro-in-TES-tih-nul): Refers to the to the stomach and intestines.

Gastrointestinal stromal tumor: GIST. A type of tumor that usually begins in cells in the wallls of the gastrointestinal tract. It can be benign or malignant.

Gastrointestinal tract (GAS-tro-in-TES-tih-nul): The stomach and intestines.

Gastroscope (GAS-tro-skope): A thin, lighted tube used to view the inside of the stomach.

Gastroscopy (gas-TRAHS-ko-pee): An examination of the inside of the stomach using a thin, lighted tube (called a gastroscope) passed through the mouth and esophagus.

Geldanamycin analogue: An antineoplastic antibiotic drug that belongs to the family of drugs called ansamycins.

GEM 231: A drug that may inhibit the growth of malignant tumors.

Gemcitabine: An anticancer drug that belongs to the family of drugs called antimetabolites.

Gemtuimetabolites: An anticancer drug that belongs to the family of drugs called antimetabolites.

Gene: The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein.

Gene deletion: The total loss or absence of a gene.

Gene therapy: The insertion of genes into an individual's cells and tissues to treat a disease, such as a hereditary disease in which a deleterious mutant allele is replaced with a functional one.

Gene-modified: Cells that have been altered to contain different genetic material than they originally contained.

Genetic: Inherited; having to do with information that is passed from parents to offspring through genes in sperm and egg cells.

Genetic counseling: A communication process between a specially trained health professional and a person and a person concerned about the genetic risk of disease. The person's family and personal medical history may be discussed, and counselling may lead to genetic testing.