gamma rays A form of radiation that comes from a radioisotope. Gamma rays are commonly used in radiotherapy and also in some radioisotope scans to treat cancer .

ganglion [gang-li-on] (pl. ganglia) A thin-walled, harmless cyst or non-cancerous swelling that may appear in the tendons or joints, especially at the wrist.

gastrectomy [gas-trec-to-my] The removal of the stomach , or of part of it, by surgery.

gastrointestinal tract [gas-tro in-tes-tin-al] The gut. It starts at the stomach and includes the large intestine and small intestine , (also called the large bowel and small bowel). See bowel.

gastroscope [gas-tro-scope] A thin, flexible, tube-like instrument that is used to see into and take photographs inside the stomach . This process is called a gastroscopy. A gastroscope can also be used to take samples of tissue for biopsy and to remove small growths: see endoscope , fibre optics .

gene The tiny factors that govern the way the body's cells grow and behave. Each person has a set of many thousands of genes inherited from both parents. Genes are found in every cell of the body.

giant cells tumour A tumour that occurs in bone. Giant cells tumours may be benign (not a cancer ) or malignant (a cancer); malignant giant cells tumours usually develop from benign ones. They most often occur in the long bones of the leg, but may occur anywhere: see bone cancer .

gland (adj. glandular) An organ or group of cells that makes certain fluids (hormones , saliva, sweat) that are used in the body or excreted.

glioblastoma [gli-o bla-sto-ma] One of the most malignant of brain tumours . It occurs in children and adults: see glioma .

glioma [gli-o-ma] Any tumour that starts in the connective tissue (the glia) of the nervous system. They range from slow-growing benign tumours to cancers that grow rapidly to invade surrounding tissues. The term is sometimes used to describe all tumours of the brain and spinal cord.

goitre A swelling in the neck due to enlargement of the thyroid gland . One form, toxic nodular goitre, sometimes develops into thyroid cancer.

graft Any organ or tissue that is transplanted to replace a part. The transplantation may come from one part of a person's body to another, or from another person.

granulocyte-colony stimulating factor (G-CSF) A protein that stimulates the growth and maturation of granulocytes.

growth factor A substance that stimulates cells to reproduce and rapidly multiply.

gynaecological oncologist [gy-nae co-log-i-cal on-col-o-gist] A doctor who specialises in treating women diagnosed with cancer of the reproductive organs.

gynaecologist [gy-nae-col-o-gist]A doctor who specialises in conditions affecting women, particularly conditions of the reproductive system.