Carcinogenesis via microbial infection

Recent progress in the field of infectious diseases involving carcinogenesis has been striking. Extensive studies of Helicobacter pylori, and hepatitis type B and C virus showed that they are the primary cause of gastric cancer and hepatoma, respectively. Also some parasites such as Opistorchis viverrini and Schistosoma haematobium are also putative causes of cholangiocarcinoma and urinary bladder cancer, respectively. All of them require a chronic infection of more than 15 years. More than 50% of Japanese cancers are thus considered to be caused by chronic infection. The classic theory of carcinogenesis is radiation, chemicals and viral infection. Recent studies in free radical and biochemical research in our infectious diseases show all carcinogenesis involves free radical generation such as superoxide (O2.-), nitric oxide (NO), and their adducts peroxynitrite (ONOO-), H2O2 hydrooxyl radical (.OH), HClO, and NO2Cl as well as alkylperoxy radicals. All these molecular species are capable of modifying nucleic acid and DNA or RNA; furthermore a strand break is frequently observed, and hence potent mutagenicity and a probable cause of cancer. Thus, the unifying theory of carcinogenesis may most likely involve the mechanism of free radicals. This means a paradigm shift is needed in the public health policy for the tactics of cancer prevention.