ABSTRACT
Cancer is a disease of dysregulated cell growth that involves excessive proliferation of cells as well as the capacity to invade tissues and metastasize to and colonize remote sites (Fenton and Longo, 1998). Nearly all cancers arise from a single cell whose uncontrolled proliferation leads to a clone of cells that appears as a recognizable tumor. This origin of a tumor from a single clone of cells is the critical feature that distinguishes a malignant neoplasm from hyperplasia or a benign growth. The aberrant cell growth results from an interplay between environmental and genetic factors. Environmental factors include exogenous agents such as chemicals (food additives, insecticides), radiation, and infectious organisms. Environmental agents exert their impact on the cell by promoting dysregulated growth at two basic levels: first, in an extragenetic fashion by functioning directly as growth factors or by stimulating the production of growth factors; or by causing physical mutations, or changes, in genes, which result in quantitative or qualitative modifications of their expression. Thus, environmental insults may impact directly on the genome to promote carcinogenesis.
