Gold, L.S., Wright, C., Bernstein, L., and de Veciana, M. Reproducibility of results in "near-replicate" carcinogenesis bioassays. J. Natl. Cancer Inst. 78: 1149-1158 (1987).
Reproducibility of results was examined in 70 "near-replicate" comparisons consisting of two or more long-term carcinogenesis bioassays of the same chemical administered by the same route and using the same sex and strain of rodent. Overall there was good reproducibility of positivity, target site and carcinogenic potency (TD50--defined in the paper) in hamsters, mice, and rats. The published authors' opinions about whether the test was positive, disagreed in only 9 of the 70 comparisons. Among the 35 comparisons in which all tests of the chemical were positive, 33 of the near-replicates had at least one identical target site. The carcinogenic potency values estimated from near-replicate tests in these 35 comparisons were within a factor of 2 of each other in 40% of the comparisons, within a factor of 5 in 80%, and within a factor of 10 in 90%. For the few cases in which the carcinogenic response was not reproduced, analyses suggest two explanations. In mice, the discrepant cases tended to have shorter experiment times than average; in both rats and mice, the discrepant results tended to be tests of weakly active compounds.
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