Strengths and weaknesses of long-term bioassays

The long-term bioassay for carcinogenic potential is a valuable tool for assessing human hazard, but suffers from severe limitations. Some of these follow directly from the use of animals as surrogates for man; others are created by study design and interpretations. It is recommended that much attention must be given to dose selection so as not to destroy the validity of the purported model and that emphasis must be placed upon elucidating the nature of the stimuli the test substance provides to the animal. Only after arriving at an understanding of the primary activity will it be possible to judge whether or not a similar response can be expected from man. The recently instituted change by the National Toxicology Program in expressing their interpretive conclusions promises a shift of the investigator's focus from the response of a test system to the action of the test substance.