Most human cancers are believed to be caused by exposure to extrinsic factors, among which chemical agents are thought to be a major contributor. These agents must be identified, evaluated, and controlled if the incidence of human cancer is to be reduced. For this reason and the fact that many of these chemicals may have great social and economic impact, it is essential that the procedures used to determine their carcinogenicity be established on the best scientific bases as are practically possible. However, differences in scientific approaches and endpoints, as well as economic considerations, exclude the use of any single set of procedures to meet the objectives of all carcinogen bioassay studies. Notwithstanding these differences, certain features are common to all well designed and properly conducted long-term animal studies.
The guidelines contained herein are used by the NCI Carcinogenesis Bioassay Program (CBP) to screen environmental and occupational chemicals for carcinogenicity by their oral administration to small rodents. However, they also may be applicable, in part or in toto, to other long-term animal studies that have different procedures, objectives, or endpoints. It is not the intent of this document to address these variations. Although there are no substitutes for good animal care practices, deviations from these guidelines may sometimes be necessary for those laboratories not specially equipped to conduct large-scale bioassay studies.