NTP carcinogens--interpretational problems

The National Toxicology Program (NTP) was established in 1978 with the broad goal of strengthening the science base of chemical toxicity, thus providing better information to regulatory and research agencies. Since that time the NTP has conducted in-depth toxicity/carcinogenesis studies on over 200 chemicals of importance to industry, the public at large and the general environment; clearly the largest such database in the world. This database is unique in that it represents an objective fairly standard accumulation of peer-reviewed information on a myriad of chemicals composed of various chemical classes, non-carcinogens as well as carcinogens. The results of these studies are reported as "no evidence, equivocal evidence, some evidence or clear evidence of carcinogenic activity" in a single sex/species. There is also an "inadequate" category for studies that have major limitations. Although noted, no attempt is made to give added weight to chemicals which cause neoplasms at multiple sites, at rare versus common sites, in both species/sexes, which occur early in the study, at low as well as high doses, or those observed in the presence or absence of toxicity (necrosis, degeneration, etc.) in the same organ. Such observational data may serve as "markers" or "alerts" for whether a chemical's in vivo carcinogenic activity is the result of mutagenic or non-mutagenic activity.