x-ray: High-energy radiation used in low doses to diagnose diseases and in high doses to treat cancer.

x-ray therapy: The use of high-energy radiation from x-rays to kill cancer cells and shrink tumors. Radiation may come from a machine outside the body (external-beam radiation therapy) or from materials called radioisotopes. Radioisotopes produce radiation and can be placed in or near the tumor or in the area near cancer cells. This type of radiation treatment is called internal radiation therapy, implant radiation, interstitial radiation, or brachytherapy. Systemic radiation therapy uses a radioactive substance, such as a radiolabeled monoclonal antibody, that circulates throughout the body. X-ray therapy is also called radiation therapy, radiotherapy, and irradiation.

xenograft: The cells of one species transplanted to another species.

xeroderma pigmentosum: A genetic condition characterized by a sensitivity to all sources of ultraviolet radiation.

xerogram: A picture of the body recorded on paper rather than on film. Also called a xeroradiograph.

xeroradiography (ZEE-ro-ray-dee-AH-gra- fee): A type of x-ray in which a picture of the body is recorded on paper rather than on film.

XR9576: A substance that is being studied for its ability to overcome tumor-cell resistance to anticancer drugs. It belongs to the family of drugs called anthranilic acid derivatives.