NCIt definition : Any chemical, biological or physical agents that increase the risk of neoplasms in
humans or animals. Carcinogens include natural or synthesized compounds, certain viruses,
and various sources of radiation. A carcinogen may directly alter the genetic material
of cells (genotoxic), thereby initiating or promoting the process of malignant transformation;
it also may induce cancers by mechanisms that do not involve a direct alteration of
cellular genetic material (non-genotoxic). (NCI04);
Alternative definition : NCI-GLOSS: Any substance that causes cancer.;