Evidence suggesting lack of carcinogenicity: There are several adequate studies covering the full
range of levels of exposure that humans are known to encounter, which are mutually consistent in not
showing a positive association between exposure to the agent and any studied cancer at any observed
level of exposure. The results from these studies alone or combined should have narrow confidence
intervals with an upper limit close to the null value (e.g. a relative risk of 1.0). Bias and confounding should
be ruled out with reasonable confidence, and the studies should have an adequate length of follow‐up. A
conclusion of evidence suggesting lack of carcinogenicity is inevitably limited to the cancer sites,
conditions and levels of exposure, and length of observation covered by the available studies. In addition,
the possibility of a very small risk at the levels of exposure studied can never be excluded.
In some instances, the above categories may be used to classify the degree of evidence related to
carcinogenicity in specific organs or tissues.