Studies of Cancer in Experimental Animals

The nature and extent of impurities or contaminants present in the chemical or mixture being evaluated are given when available. Animal strain, sex, numbers per group, age at start of treatment and survival are reported. 

Other types of studies summarized include experiments in which the agent or mixtme was administered in conjunction with known carcinogens or factors that modify carcinogenic effects studies in which the end-point was not cancer but a defined precancerous lesion and experiments on the carcinogenicity of known metabolites and derivatives. 

For experimental studies of mixtmes, consideration is given to the possibility of changes in the physicochemical properties of the test substance during collection, storage, extraction, concentration and delivery. Chemical and toxicological interactions of the components of mixtmes may result in nonlinear dose-response relationships. 

As mentioned earlier (p. 11), the Monographs are not intended to summarize all published studies. Those studies in experimental animals that are inadequate (e g., too short a duration, too few animals, poor survival see below) or are judged irrelevant to the evaluation are generally omitted. Guidelines for conducting adequate long-term carcinogenicity experiments have been outlined (e.g. Montesano et al, 1986). 

Considerations of importance to the Working Group in the interpretation and evaluation of a particular study include (i) how clearly the agent was defined and, in the case of mixtures, how adequately the sample characterization was reported (ii) whether the dose was adequately monitored, particularly in inhalation experiments (iii) whether the doses and duration of treatment were appropriate and whether the survival of treated animals was similar to that of controls (iv) whether there were adequate numbers of animals per group (v) whether animals of each sex were used (vi) whether animals were allocated randomly to groups (vii) whether the duration of observation was adequate and (viii) whether the data were adequately reported. If available, recent data on the incidence of specific tumours in historical controls, as 

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