Rodent cancer bioessays

Rodent cancer bioessays explained

Mainstream medical journal ATLA has this year published a paper reviewing animal use to identify cancer-causing materials.  The paper (in ATLA 34, 19-27, 2006) compares animal-based data from the USAs EPA with the World Health Organisation data - which is usually human based.


One conclusion is that that animal data is usually insufficient to lead to a suggestion as to whether a chemical is a probable, definite or even possible human carcinogen.  Of 160 chemicals with insufficient human data, 93 (58%) were unclassified based on animal studies.  When classifications from the two sources were compared, they were found to classify chemicals similarly only when there was human data.  Animal data alone leads to different conclusions as the results can’t be interpreted.


A statistical analysis was done of 502 chemicals that were carcinogens in animals.   Of these, 398 (79%) were NOT definite or probable human carcinogens.  Given the tendency of animals to be used to confirm that which is already known, many of the remaining 21% that were classified as carcinogens in animals and humans are subject to suspect procedure.  Certainly the findings show that four out of five animal carcinogens are considered by experts NOT to be human carcinogens.


The consistent way animal tests predict risks that are not relevant to humans has been found to be true of animal testing for drug side effects too.  In carcinogen identification, other experts have noted that animals falsely identify risks at an alarming rate. $250 million is spent annually on these tests.


The writers state that “the conventional rodent bioessay [tests for carcinogens] has never been formally validated against human data.  On the contrary, validation studies have found the rodent bioessay to be lacking in human specificity (i.e. the ability to detect human non-carcinogens)…or even human sensitivity (i.e. the ability to detect human carcinogens at all)….Ennever and Lave showed that neither of the two commonly-used interpretations of rodent carcinogenicity data provide conclusions about human carcinogenicity that are supported by existing data.”