How are carcinogenic substances classified?
Action of chemical substances on organs: carcinogenesis

A substance is carcinogenic when it causes an increase in the incidence of malignant tumors or a decrease in the time to tumor onset.

The assessment of these effects is based primarily on the results of long-term animal studies; it is preferable to have results from two different species.

The preferred species for carcinogenicity testing are rats and mice. The study should generally cover most of the normal lifespan of the experimental animals, i.e., approximately 24 months. The results are evaluated using an appropriate statistical method. Secondary information may be used in the evaluation of carcinogenic potential, such as data on genotoxicity, metabolic or biochemical studies, the induction of benign tumors, and structural relationships with other known carcinogens.

Certain arguments diminish the significance of experimental tumor induction, such as:

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