Harmonic Mean of LTD₁₀

In the Excel spreadsheet, an LTD₁₀ value is reported for a chemical in each species with a positive evaluation of carcinogenicity by the author of at least one experiment. If there is only one positive test on the chemical in the species, then the most potent LTD₁₀ value from that test is reported. When more than one experiment is positive, in order to use all the available data, the reported LTD₁₀ value is a harmonic mean of the most potent LTD₁₀ values from target sites in each positive experiment.

To obtain the harmonic mean, the lowest LTD₁₀ value from each positive experiment is selected from among positively evaluated target sites with a statistically significant dose response (two-tailed p<0.1). If no positive sites have a significant dose response, then the most potent (lowest LTD₁₀) is selected from among positively evaluated sites with p≥0.1. If some experiments in a species have a positive evaluation and statistically significant results while others have only positive evaluations but statistically non-significant results (p≥0.1), the non-significant experimental results are not used in the calculation of the harmonic mean.

Forty-four chemicals had an experiment for which no LTD₁₀ could be estimated because all dosed animals had the tumor of interest, and only summary data on tumor incidence were available. For these cases the 99% upper confidence limit of LTD₁₀ is used in the harmonic mean as a replacement for the LTD₁₀. These cases are marked in the table with a “P” superscript. For 9 of these chemicals, all animals had tumors at the target site in all positive experiments. The 99% upper confidence limit replaces a harmonic mean in these cases, and the reported value is marked with a “<” symbol to indicate that any LTD₁₀ value would be lower.

References

1. Gold, L.S., Slone, T.H., and Bernstein, L. Summary of carcinogenic potency (TD₅₀) and positivity for 492 rodent carcinogens in the Carcinogenic Potency Database. Environ. Health Perspect. 79: 259-272 (1989). Abstract Text
2. Gold, L.S., Slone, T.H., and Ames, B.N. Overview of analyses of the Carcinogenic Potency Database. In: Gold, L.S., and Zeiger, E., Eds. Handbook of Carcinogenic Potency and Genotoxicity Databases. Boca Raton, FL: CRC Press, 1997, pp. 661-685.
3. Gold, L. S., Slone, T. H., and Ames, B. N. What do animal cancer tests tell us about human cancer risk? Overview of analyses of the Carcinogenic Potency Database. Drug Metabolism Reviews 30: 359-404 (1998). Abstract PDF

Return to the Carcinogenic Potency Project (CPDB) Home Page:

Last updated: August 6, 2007