Cancer medicine, 7th edition. Hamilton, Ontario, Canada: B C Decker Inc, 2006 Feb; :1-13
Human chemical carcinogenesis is a multistage process that results from exposures, usually in the form of complex chemical mixtures, often encountered in the environment or through our lifestyle and diet (Table 14-1). A prime example is tobacco smoke, which can cause cancers at multiple sites, including the lung, bladder, head, and neck. Although most chemical carcinogens do not react directly with intracellular components, they are activated to carcinogenic and mutagenic electrophiles by metabolic processes evolutionary designed to rid the body of toxins and to modify endogenous compounds. Electrophilic chemical species are naturally attracted to nucleophiles like DNA and protein, and through covalent bonding to deoxyribonucleic acid (DNA) genetic damage results. Once internalized, carcinogens are subject to competing processes of metabolic activation and detoxication, although some chemical species can act directly.