Definition
Chemical carcinogenesis is commonly defined to indicate the initiation or development of neoplasia by chemicals. It comprises not only epithelial malignancies (carcinomas) but also mesenchymal malignant tumors (sarcomas).
People can be exposed to carcinogens which are present in food, air, or water. In addition, some carcinogens are created within the body as products of metabolism or certain pathophysiologic states like inflammation or oxidative stress. Carcinogens from the environment likely contribute to a large percent of human cancers when related to lifestyle, including diet and tobacco use.
Chemical carcinogenesis is a multistage process. Carcinogenic chemicals act by introducing certain genetic changes in a cell (initiation), promoting the foundation of a benign neoplasm (promotion), converting the
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1. Co-carcinogens
These substances are not carcinogenic on their own but can enhance the effects of genotoxic carcinogens when given simultaneously. They may increase the concentration of the initiator or the reactive metabolite. This can be achieved by an increase of the carcinogen absorption or bio activation or a decrease of the elimination of the initiator by inhibiting the detoxification enzymes or depleting the endogenous substrates involved in phase II reactions, such as glutathione. Co carcinogens may inhibit the rate of DNA repair, or they may enhance conversion of DNA lesions to permanent alterations.
Tobacco smoke contains relatively small amounts of genotoxic carcinogens, such as PAH and nitrosamines; its marked carcinogenic effects are perhaps attributed to catechols which act as co-carcinogens.
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