A substance or agent that can cause cells to become cancerous by altering their genetic structure so that they multiply continuously and become malignant. Exposure to chemicals, whether naturally occurring or industrially produced, is a constant and inescapable fact of life. While the vast majority of these chemical compounds are beneficial or completely harmless. Most of cellular genetics leads to cancer development and along with metabolic activity. Chemical-induced genetic and metabolic alterations are attributable to their deleterious effect on DNA repair, gene expression, activation of proto-oncogenes, and inhibition of tumor suppressor genes. Impaired cellular DNA damage is mediated primarily by two distinct kinase dependent pathways, namely the Ataxia Telangiectasia Mutated (ATM) and ataxia telangiectasia and Rad3-related (ATR). Effect of chemical carcinogens on genetic integrity and metabolic pathways is largely dependent upon and modulated by a variety of factors. These include host susceptibility age, race, gender, polymorphisms of carcinogen metabolism genes etc.