2nd International Symposium on Genotoxic and Carcinogenic Thresholds

Abstract

Since the disaster at the Fukushima No. 1 nuclear power plant in March 2011, people became concerned about adverse eSects of radiation, in particular those of low dose radiation strongly. The eSects of radiation on chromosome DNA are stochastic events, and thus it is thought that radiation poses cancer risk to humans even at very low doses. Likewise, genotoxic compounds, which interact with DNA and induce mutations, are assumed to have no thresholds for their action. These compounds are used to be called ``radiomimetic compounds''. Hence, genotoxic carcinogens, which induce cancer via genotoxic mechanisms such as mutations, are regulated based on a paradigm that they have no thresholds for the cancer risk. Recently, however, the paradigm has been challenged by research on analyzes of carcinogenicity and genotoxicity of chemicals at low doses. In addition, organisms including humans possess various self-defense mechanisms, such as detoxication metabolism, DNA repair, error-free translesion DNA synthesis and apoptosis etc, which may suppress genotoxicity of chemicals at low doses and reduce the mutation frequency and cancer risk to spontaneous levels. These self defense mechanisms may constitute ``apparent'' or ``practical'' thresholds for genotoxic carcinogens. To discuss the low dose eSects of genotoxic and carcinogenic compounds and the implication in regulatory toxicology, the second international symposium on genotoxic and carcinogenic thresholds was held on November 23, 2011 in Tokyo. In this symposium, six and four experts of genotoxicity and chemical carcinogenicity were invited from inside and outside of Japan, respectively, to discuss genotoxicity and carcinogenicity of chemicals at low doses and the regulatory policies. This symposium follows the precedent symposia ``International symposium—threshold of carcinogenicity and genotoxicity'' in Kobe in Japan in 2006, and ``the 1st International symposium on genotoxic and carcinogenic thresholds'' in Tokyo in 2008. Here, we summarize the presentations of the symposium to discuss future perspectives of research on genotoxic and carcinogenic thresholds.