Radiation-associated cancer
	With the exception of tobacco, ionizing radiation is probably the most studied carcinogen, however, it is not yet possible to determine whether or not a specific cancer was induced by radiation. Epidemiological studies provide the primary data on cancer risk in man after exposure to ionizing radiation. Free radicals, produced by ionizing radiation through the deposition of energy in water, is known to induce acute and late radiation effects. The highly reactive free radicals interact with cell organelles as the cell membrane and DNA. Damage to these organelles initiates the biological response necessary for carcinogenesis, and since free radicals produced by ionizing radiation mimics the biological response of other pathogenic processes such as inflammation and ultraviolet light, it is not possible to determine whether a specific cancer was induced by ionizing radiation or not. However, on the assumption that ionizing radiation causes specific genetic lesions, e.g. oncogen activation and/or tumor subpressor gene inactivation, there will hopefully be possibilities to characterize radiation-induced malignant clones in the future.