The enigma of classification

Group A Human carcinogen. This group is used only when there is sufficient evidence from epidemiologic studies to support a causal association between exposure to the agents and cancer. 

Group C Possible human carcinogen. This group is used for agents with limited evidence of carcinogenicity in animals in the absence of human data. It includes a wide variety of evidence, e.g., 

Group D Not classifiable as to human carcinogenicity. This group is used for agents with inadequate human and animal evidence of carcinogenicity or for which no data are available. 

Group E Evidence of non-carcinogenicity for humans. This group is used for agents that show no evidence for carcinogenicity in at least two animal tests in different species or in both adequate epidemiologic and animal studies. 

The designation of an agent as being in Group E is based on the available evidence and should not be interpreted as a definitive conclusion that the agent will not be a carcinogen under any circumstances. 

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