Module 3: Toxicology - Section 13: Occupational Carcinogenesis
TOX 13.13: Carcinogen Exposure Assessment

INTERNATIONAL AGENCY FOR RESEARCH ON CANCER (IARC) CLASSIFICATION OF CARCINOGENS:

The IARC has a monographs programme in which agents, mixtures and exposure circumstances are evaluated if there is evidence of human exposure,  and human or animal data on carcinogenicity.Evaluation of evidence of carcinogenicity in the IARC Monographs programme

1. The evidence for the induction of cancer in humans, which obviously plays an important role in the identification of human carcinogens is considered. Three types of epidemiological studies contribute to an assessment of carcinogenicity in humans: cohort studies, case-control studies and correlation (or ecological) studies. Case reports of cancer in humans may also be reviewed. The evidence relevant to carcinogenicity from studies in humans is classified into one of the following categories:

2. Studies in which experimental animals (mainly rodents) are exposed chronically to potential carcinogens and examined for evidence of cancer are reviewed and the degree of evidence of carcinogenicity is then classified into categories similar to those used for human data.

3. Data on biological effects in humans and experimental animals that are of particular relevance are reviewed. These may include toxicological, kinetic and metabolic considerations and evidence of DNA binding, persistence of DNA lesions or genetic damage in exposed humans. Toxicological information, such as that on cytotoxicity and regeneration, receptor binding and hormonal and immunological effects, and data on structure-activity relationship are used when considered relevant to the possible mechanism of the carcinogenic action of the agent.

4. The body of evidence is considered as a whole, in order to reach an overall evaluation of the carcinogenicity to humans of an agent, mixture or circumstance of exposure and translated to the classification system below:

Table 2. IARC Monograph programme classification groups for Human Carcinogenicity
Group    
    Human Animal Other 1987 19913 2002
1 The agent (mixture) is carcinogenic to humans. The exposure circumstance entails_exposures that are carcinogenic to humans. S     130 67 88 including (63 agents, 12 mixtures and 13 exposure circumstances)
2A

The agent (mixture) is probably carcinogenic to humans. The exposure  circumstance entails exposures that are probably carcinogenic to humans.

 
L
L
S

S

Strong
Strong
37 1313 64   including (1313 agents, 13 mixtures and 4 exposure circumstances)
2B

The agent (mixture) is possibly carcinogenic to humans. The exposure circumstance entails exposures that are possibly carcinogenic to humans.

 
L
I
I
L/I
S
L
Supporting 1139 214 236  including (221 agents, 12 mixtures and 4 exposure circumstances)
3

  The agent (mixture, exposure circumstance) is riot classifiable as to its carcinogenicity to humans.

 
I L/I   381 4138 496  including (477 agents, 12 mixtures and 7 exposure circumstances)
4

The agent (mixture, exposure circumstance) is probably not carcinogenic to humans.

 
LC
I
LC
LC
Strong 1 1 1
S = sufficient     L = limited     I = inadequate     LC = lack of carcinogenicity  



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Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za. Last updated Jan 2007.
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