The first target of radiation carcinogenesis is not DNA

There have been several reports showing contradictory data on the correlation between radiation-induced somatic mutations and cancer. In addition, it has recently been reported that non-DNA target effects, such as bystander effect and delayed effect, may play an important role in the process of radiation-carcinogenesis. These phenomena may be related to epigenetic changes induced by ionizing radiation. We have studied the mechanism of radiation carcinogenesis with the hypothesis that epigenetic cellular changes induced by ionizing radiation may be the first step in radiation-induced carcinogenesis. Recently, from our data, we reached the conclusion that “mutation is not direct origin of carcinogenesis.” We speculate a radiation cancer-causing target is protein. If this hypothesis is right, we cannot evaluate risk of radiation carcinogenesis by DNA target theory.