Synopsis: A list of currently known carcinogens, substances, chemicals, and products known to cause cancer in humans.
What is a Carcinogen?
A Carcinogen is defined as any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substances are considered carcinogens, but their carcinogenic activity is attributed to the radiation, for example gamma rays and alpha particles, which they emit. Common examples of non-radioactive carcinogens are inhaled asbestos, certain dioxins, and tobacco smoke. Although the public generally associates carcinogenicity with synthetic chemicals, it is equally likely to arise in both natural and synthetic substances. Carcinogens are not necessarily immediately toxic, thus their effect can be insidious.
Recently Added Carcinogens
Four substances have been added in the U.S. Department of Health and Human Services 13th Report on Carcinogens, a science-based document that identifies chemical, biological, and physical agents that are considered cancer hazards for people living in the United States. The new report now includes 243 listings.
Ortho-toluidine, used to make rubber chemicals, pesticides, and dyes, has been reevaluated and is now listed as a known human carcinogen.
Three substances have been added as reasonably anticipated to be human carcinogens. These include:
1-bromopropane, used as a cleaning solvent and spray adhesive;
cumene, used to make phenol and acetone, and also found in fuel products and tobacco smoke;
wood preservative mixture pentachlorophenol.
Health hazard sign.
"Identifying substances in our environment that can make people vulnerable to cancer will help in prevention efforts," said Linda Birnbaum, Ph.D., director of the National Institute of Environmental Health Sciences (NIEHS) and the National Toxicology Program (NTP). "This report provides a valuable resource for health regulatory and research agencies, and it empowers the public with information people can use to reduce exposure to cancer causing substances."
The Report on Carcinogens is a congressionally mandated report prepared for the HHS Secretary by NTP. The report identifies agents, substances, mixtures, or exposures in two categories: known to be a human carcinogen and reasonably anticipated to be a human carcinogen. The new report is available at ntp.niehs.nih.gov/go/roc13
A listing in the report indicates a cancer hazard, but does not by itself mean that a substance will cause cancer. Many factors, including the amount and duration of exposure, and an individual's susceptibility to a substance, can affect whether a person will develop cancer.
Estrogen-progestogen oral contraceptives (combined) (Note: There is also convincing evidence in humans that these agents confer a protective effect against cancer in the endometrium and ovary)
Ethanol in alcoholic beverages
Etoposide in combination with cisplatin and bleomycin
Fission products, including strontium-90
Haematite mining (underground)
Helicobacter pylori (infection with)
Hepatitis B virus (chronic infection with)
Hepatitis C virus (chronic infection with)
Human immunodeficiency virus type 1 (HIV-1) (infection with)
Human papilloma virus (HPV) types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59 (infection with) (Note: The HPV types that have been classified as carcinogenic to humans can differ by an order of magnitude in risk for cervical cancer)
Human T-cell lymphotropic virus type I (HTLV-1) (infection with)
Radionuclides, alpha-particle-emitting, internally deposited (Note: Specific radionuclides for which there is sufficient evidence for carcinogenicity to humans are also listed individually as Group 1 agents)
Radionuclides, beta-particle-emitting, internally deposited (Note: Specific radionuclides for which there is sufficient evidence for carcinogenicity to humans are also listed individually as Group 1 agents)
Since 1983, ortho-toluidine has been listed in the Report on Carcinogens as reasonably anticipated to be a human carcinogen. However, new cancer studies led NTP to reevaluate and reclassify ortho-toluidine, and it is now added to the category of known to be a human carcinogen, based on studies in humans showing it causes urinary bladder cancer. Ortho-toluidine is a synthetic chemical produced in other countries and imported into the United States by several companies in high volumes. It is primarily used to make rubber chemicals, pesticides, and dyes. It is also used in some consumer and medical products. People are mainly exposed through the workplace, by skin contact and/or inhalation when using ortho-toluidine. People can also be exposed outside the workplace through sources such as tobacco smoke.
3 Substances Added to the New Report as Reasonably Anticipated to Be a Human Carcinogen
The chemical 1-bromopropane is a colorless to pale yellow liquid used as a solvent in many commercial industries. It is used as a cleaner for optics, electronics, and metals, as well as a solvent for aerosol-applied adhesives such as those used in foam cushion manufacturing. It is also used in dry cleaning and in solvent sprays for aircraft maintenance. Workers in certain occupations may be more exposed to 1-bromopropane than the general population. No human studies were identified that evaluated the relationship between human cancer and exposure specifically to 1-bromopropane. However, inhalation exposure to 1-bromopropane in rodents caused tumors in several organs, including the skin, lungs, and large intestine.
Cumene is a flammable and volatile liquid with a gasoline-like odor. It is a natural component of coal tar and petroleum, and is found in tobacco smoke. It is used primarily to make acetone and phenol. People are mainly exposed to cumene through the environment and in workplaces that use or produce cumene. It can be found in emissions from petroleum products. Inhalation exposure to cumene caused lung tumors in male and female mice, and liver tumors in female mice. No human studies were identified that looked at the relationship between human cancer and exposure specifically to cumene.
Pentachlorophenol and by-products of its synthesis are complex mixtures of chemicals used as wood preservatives. Because virtually everyone who is exposed to pentachlorophenol is also exposed to its synthesis by-products, they were evaluated together. In the United States, pentachlorophenol has been regulated since the 1980s as a restricted-use pesticide. It is used industrially for treating utility poles, wood pilings, fence posts, and lumber or timber for construction. Most exposure has occurred in settings where workers treat lumber or come in contact with treated lumber. People may also be exposed to this mixture from breathing contaminated air or dust, or from contact with contaminated soil. Exposure to this mixture was associated with an increased risk of non-Hodgkin lymphoma in studies in humans. It also caused tumors in the liver and other organs in mice.
International Agency for Research on Cancer (IARC). Agents Classified by the IARC Monographs, Volumes 1 - 100. 2011.
US Department of Health and Human Services. Public Health Service, National Toxicology Program. Report on Carcinogens, Twelfth Edition. 2011.
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