Extrapolating from Specific Scientific Findings, Several Independent Laboratories

While historically, multiple studies of carcinogenicity in experimental animals may have been conducted on a single test agent in several independent laboratories, today the massive expense involved in rigorous testing for carcinogenicity in experimental animals often means that only one or two well conducted studies of carcinogenicity (often in one strain of rat and/or one strain of mouse, and typically involving males and females) may be available in the peer-reviewed literature or from government agency reports that are publicly available.

Good laboratory practice

As indicated in the Preamble, such studies, ideally conducted under good laboratory practice, may be able to establish sufficient evidence of carcinogenicity in experimental animals, depending upon the nature of results obtained.

Again, in relation to “single studies” as outlined above, when the test agent is a complex mixture, exemplified, for example, by an herbal product, it may not be possible to assume that the agent being tested is identical to either the material marketed under the same name and/or material tested in other studies that might otherwise be understood to indicate possible mechanism(s) of carcinogenesis or to exclude particular mechanism(s) of carcinogenesis.


As indicated in the Preamble, the IARC Monographs evaluations are wholly dependent on publicly available data that are exemplified by published research results in the peer-reviewed literature. This information comprises only a subset of data on pharmaceutical drugs, specifically excluding “commercial in-confidence” findings of the type provided by industry to national or multinational regulatory authorities in the context of applications to market particular drugs. The initiatives of the European Medicines Agency and other organizations to make such data publicly available are properly noted in this context.

Considerations beyond Hazard Identification

Many (if not most) regulatory decisions concerning putative carcinogens necessitate consideration not only of perceived hazard, but also of potential benefit. It is crucial, therefore, that regulatory decisions affecting drug availability include assessment not only of potential carcinogenicity (and other adverse effects), but also of the health benefits derived from their usage.