Classification of IARC

*1 Cancers in humans?

Sufficient evidence:

• Causal relationship has been established
• Chance, bias, and confounding could be ruled out with reasonable confidence

Limited evidence:

• Causal interpretation is credible
• Chance, bias, or confounding could not be ruled out

Inadequate evidence: Studies permit no conclusion about a causal association

Evidence suggesting lack of carcinogenicity:

• Several adequate studies covering the full range of exposure levels are mutually consistent in not showing a positive association at any observed level of exposure
• Conclusion is limited to the cancer sites and conditions studied

*2 Cancers in animals?

Sufficient evidence: Causal relationship has been established through either:

• Multiple positive results (2+ species, studies, or sexes of GLP study)
• Single unusual result (incidence, site/type, age at onset, or multi-site)

Limited evidence: Data suggest a carcinogenic effect but: (e.g.) from a single study, unresolved questions, benign tumours only, promoting activity only

Inadequate evidence: Studies permit no conclusion about a carcinogenic effect

Evidence suggesting lack of carcinogenicity:

• Adequate studies in at least two species show that the agent is not carcinogenic
• Conclusion is limited to the species, tumour sites, age at exposure, and conditions and levels of exposure studied