Significance of the genotoxic activities observed in vitro for 35 of 70 NTP noncarcinogens.

A speculative analysis is presented of the in vitro genotoxicity data reported by Shelby and Stasiewicz for 70 chemicals defined as noncarcinogenic to rodents by the National Toxicology Program. It is concluded that the genotoxic activities observed are probably subject to logical explanation. It is suggested that short-term genotoxicity assays conducted in vivo on newly defined in vitro genotoxins may have a useful role to play in discriminating animal carcinogens from noncarcinogens. It is clear from the results reported that genotoxic activities observed in vitro for a new test chemical only provide evidence of its possible animal carcinogenicity; they are not definitive of carcinogenicity--the difference may be negligible in general but might prove unacceptable in the particular.