Oxidative mechanisms in carcinogenesis.

Cancer in humans and animals is a multistep disease process. In this process, a single cell can develop from an otherwise normal tissue into a malignancy that can eventually destroy the organism. The complex series of cellular and molecular changes that occur through the development of cancers can be mediated by a diversity of endogenous and environmental stimuli. Active oxygen species and other free radicals have long been known to be mutagenic; further, these agents have more recently emerged as mediators of the other phenotypic and genotypic changes that lead from mutation to neoplasia. Free radical production is ubiquitous in all respiring organisms, and is enhanced in many disease states, by carcinogen exposure, and under conditions of stress. Free radicals may therefore contribute widely to cancer development in humans. This review explores the molecular mechanisms through which free radicals can participate in the carcinogenic process.