Section: 16 | Chemical Carcinogens |

How to Cite this Reference

Chemical Carcinogens

Maria J. Doa

The following chemical substances are listed in the 14th Report on Carcinogens, 2016, released by the National Institute of Environmental Health Sciences (NIEHS) under the National Toxicology Program (NTP) (Ref. 1); or in the World Health Organization's International Research on Cancer (IARC) Monographs on the Identification of Carcinogenic Hazards to Humans (Volumes 1-124) (Ref. 2); or in both.

Substances are grouped in two classes as defined in the NTP report:

"Known to be human carcinogens: There is sufficient evidence of cancer from studies in humans showing a cause-and-effect relationship between exposure to the substance and human cancer.
Reasonably anticipated to be human carcinogens: There is limited evidence of carcinogenicity from studies in humans, which indicates that causal interpretation is credible, but that alternative explanations, such as chance, bias, or confounding factors, could not adequately be excluded,
OR

there is sufficient evidence of carcinogenicity from studies in experimental animals, which indicates there is an increased incidence of malignant and/or a combination of malignant and benign tumors (1) in multiple species or at multiple tissue sites, or (2) by multiple routes of exposure, or (3) to an unusual degree with regard to incidence, site, or type of tumor, or age at onset,

OR

there is less than sufficient evidence of carcinogenicity in humans or laboratory animals; however, the agent, substance, or mixture belongs to a well-defined, structurally related class of substances whose members are listed in a previous Report on Carcinogens as either known to be a human carcinogen or reasonably anticipated to be a human carcinogen, or there is convincing relevant information that the agent acts through mechanisms indicating it would likely cause cancer in humans.

Conclusions regarding carcinogenicity in humans or experimental animals are based on scientific judgment, with consideration given to all relevant information. Relevant information includes, but is not limited to, dose response, route of exposure, chemical structure, metabolism, pharmacokinetics, sensitive sub-populations, genetic effects, or other data relating to mechanism of action or factors that may be unique to a given substance. For example, there may be substances for which there is evidence of carcinogenicity in laboratory animals, but there are compelling data indicating that the agent acts through mechanisms which do not operate in humans and would therefore not reasonably be anticipated to cause cancer in humans.

IARC classifies substances as:

Group 1 Carcinogenic to humans: This category applies whenever there is sufficient evidence of carcinogenicity humans. In addition, this category may apply when there is both strong evidence in exposed humans that the agent exhibits key characteristics of carcinogens and sufficient evidence of carcinogenicity in experimental animals.
Group 2A Probably carcinogenic to humans: This category generally applies when at least two of the following evaluations have been made, including at least one that involves either exposed humans or human cells or tissues:
- Limited evidence of carcinogenicity in humans,
- Sufficient evidence of carcinogenicity in experimental animals,
- Strong evidence that the agent exhibits key characteristics of carcinogens.

If there is inadequate evidence regarding carcinogenicity in humans, there should be strong evidence in human cells or tissues that the agent exhibits key characteristics of carcinogens. If there is limited evidence of carcinogenicity in humans, then the second individual evaluation may be from experimental systems (i.e., sufficient evidence of carcinogenicity in experimental animals or strong evidence in experimental systems that the agent exhibits key characteristics of carcinogens).

Group 2B Possibly carcinogenic to humans
Group 3 Not classifiable as to its carcinogenicity to humans

Only substances classified by IARC as Groups 1 and 2A are included in this list.

The NTP report and IARC monographs also list many poorly defined materials such as soots, tars, mineral oils, and coke oven emissions, as well as viruses, sunlight, ionizing radiation, etc. These substances are not included here.

Additional substances are evaluated by NTP on an ongoing basis but are not added to the list below until issued in its next formal report. See details in Ref. 1.

The table is ordered by the substance name normally used in the CRC Handbook. In many cases the primary name given here is different from that used in the NTP report and/or the IARC monographs; however, names used in the NTP report and/or the IARC monographs appear in the Synonym or Comments columns. Additional information and acronyms for the compounds are given in the Comments column. The substances classified by NTP as known carcinogens and those classified by IARC as Class 1 Carcinogenic to Humans are listed first.

Extensive details on each substance and of the classification approaches are given in the references.

References

14th Report on Carcinogens, <http://ntp.niehs.nih.gov/pubhealth/roc/index-1.html>, 2019.
IARC Monographs on the Identification of Carcinogenic Hazards to Humans, Vols. 1-124, <https://monographs.iarc.fr/agents-classified-by-the-iarc/>, 2019.

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Chemicals Classified by NTP and IARC

Name	Synonym	Mol. form.	CAS Reg. No.	Comments	NTP Classification	IARC Classification
Continued on next page...
NTP Known to Be Human Carcinogens and/or IARC Group 1
Aflatoxins			1402-68-2		Known to be human carcinogens	Group 1
4-Aminobiphenyl	p-Biphenylamine	C₁₂H₁₁N	92-67-1		Known to be human carcinogens	Group 1
Aristolochic acids					Known to be human carcinogens	Group 1
Arsenic		As	7440-38-2	and inorganic arsenic compounds	Known to be human carcinogens	Group 1
Asbestos			1332-21-4	IARC: all forms, including actinolite, amosite, anthophyllite, chrysotile, crocidolite, tremolite)	Known to be human carcinogens	Group 1
Azathioprine	6-[(1-Methyl-4-nitro-1H-imidazol-5-yl)thio]-1H-purine	C₉H₇N₇O₂S	446-86-6		Known to be human carcinogens	Group 1
Benzene	[6]Annulene	C₆H₆	71-43-2		Known to be human carcinogens	Group 1
p-Benzidine	[1,1'-Biphenyl]-4,4'-diamine	C₁₂H₁₂N₂	92-87-5	includes dyes metabolized to benzidene	Known to be human carcinogens	Group 1
Benzo[a]pyrene	2,3-Benzopyrene	C₂₀H₁₂	50-32-8		Reasonably anticipated to be human carcinogens	Group 1
Beryllium	Glucinium	Be	7440-41-7	and beryllium compounds	Known to be human carcinogens	Group 1
Bis(2-chloroethyl) sulfide	Mustard gas	C₄H₈Cl₂S	505-60-2	listed by NTP as mustard gas; listed by IARC as sulfur mustard	Known to be human carcinogens	Group 1
Bis(chloromethyl) ether	Chloromethyl ether	C₂H₄Cl₂O	542-88-1	and technical grade chloromethyl methyl ether	Known to be human carcinogens	Group 1
1,3-Butadiene	Divinyl	C₄H₆	106-99-0		Known to be human carcinogens	Group 1
1,4-Butanediol dimethylsulfonate	Busulfan	C₆H₁₄O₆S₂	55-98-1		Reasonably anticipated to be human carcinogens	Group 1
Cadmium		Cd	7440-43-9	and cadmium compounds	Known to be human carcinogens	Group 1
Chlorambucil		C₁₄H₁₉Cl₂NO₂	305-03-3		Known to be human carcinogens	Group 1
Chloroethene	Vinyl chloride	C₂H₃Cl	75-01-4		Known to be human carcinogens	Group 1
1-(2-Chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea	Semustine	C₁₀H₁₈ClN₃O₂	13909-09-6	also known as MeCCNU	Known to be human carcinogens	Group 1
Chloromethyl methyl ether		C₂H₅ClO	107-30-2		Known to be human carcinogens	Group 1

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