The Role of the Apoptotic Machinery in Ionizing Radiation-Induced Carcinogenesis

Ionizing radiation is an established cause of cancer based on epidemiologic and experimental evidence. According to epidemiological data, virtually all tissues in the human body are sensitive to the carcinogenic action of radiation. Apoptosis represents a major barrier to cancer because apoptotic cell death eliminates dangerous cells that may initiate tumor development. The explosion in research on apoptosis in the 1990s has demonstrated that irradiated cells have differential apoptotic proclivities and has suggested that radiation can affect apoptosis by inducing the type of damage that is eliminated by programmed cell death but may also modulate the efficiency of this damage removal process. The purposes of this review are to summarize some earlier studies on carcinogenesis that serve as a reminder of the background on which more recent studies are based, to highlight examples of progress in cancer and apoptosis research in the context of radiation carcinogenesis, to indicate gaps in our knowledge, and to point out possibly fertile directions for future investigation.