The term<unk>  refers to any substance, radionuclide or radiation which is an agent directly involved in the promotion of cancer or in the facilitation of its propagation. This may be due to genomic instability or to the disruption of cellular metabolic processes. Several radioactive substances are considered<unk> s, but their<unk> ic activity is attributed to the radiation, for example gamma rays or alpha particles, which they emit. Common examples of<unk> s are inhaled asbestos and tobacco smoke.
Cancer is a disease where damaged cells of the patient's body do not undergo programmed cell death, but their growth is no longer controlled and their metabolism is altered.<unk> s may increase the risk of getting cancer by altering cellular metabolism or damaging DNA directly in cells, which interferes with biological processes, and induces the uncontrolled, malignant division ultimately leading to the formation of tumors. Usually DNA damage, if too severe to repair, leads to programmed cell death, but if the programmed cell death pathway is damaged, then the cell cannot prevent itself from becoming a cancer cell.
There are many natural<unk> s. Aflatoxin B1, which is produced by the fungus Aspergillus flavus growing on stored grains, nuts and peanut butter, is an example of a potent, naturally-occurring microbial<unk> . Certain viruses such as Hepatitis B and human papilloma viruses have been found to cause cancer in humans. The first one shown to cause cancer in animals was Rous sarcoma virus, discovered in 1910 by Peyton Rous.
Benzene, kepone, EDB, asbestos, and the waste rock of oil shale mining have all been classified as<unk> ic.As far back as the 1930s]], industrial and tobacco smoke were identified as sources of dozens of<unk> s, including benzopyrene, tobacco-specific nitrosamines such as nitrosonornicotine, and reactive aldehydes such as formaldehyde — which is also a hazard in embalming and making plastics. Vinyl chloride, from which PVC is manufactured, is a<unk>  and thus a hazard in PVC production.
Co-carcinogens are chemicals which do not separately cause cancer, but do so in specific combinations.
After the<unk>  enters the body, the body makes an attempt to eliminate it through a process called biotransformation. The purpose of these reactions is to make the<unk>  more water-soluble so that it can be removed from the body. But these reactions can also convert a less toxic<unk>  into a more toxic one.
DNA is nucleophilic, therefore soluble carbon electrophiles are<unk> ic, because DNA attacks them. For example, some alkenes are toxicated by human enzymes to produce an electrophilic epoxide. DNA attacks the epoxide, and is bound permanently to it.  This is the mechanism behind the<unk> ity of benzopyrene in tobacco smoke, other aromatics, aflatoxin and mustard gas.
Carcinogen
Food additive
Toxic metal
Biological pigment
Pesticide
Inhalant
Phytochemical
Microorganism