The Statistical Analysis of In-Vitro Chromosome Aberration Assay

The purpose of in-vitro chromosome aberration assay (ABS) is to determine whether the test compound is a clastogen which induces structural changes in chromosomes. The ABS belongs to the standard three test battery for genotoxicity testing for pharmaceuticals recommended by the fourth International Conference on Harmonisation (1997, Brussel). A full account of biological details of this assay can be found in Galloway et al (1994). The standard design consists of a negative control and at least three positive dose groups. At each dose a sample, say 200, of metaphase cells is examined microscopically and cells exhibiting at least one type of chromosome aberration are identified. It has been well established that that binomial sampling model can be adopted for proportions of cells with chromosome aberration. (Margolin et al, 1986, Richardson et al , 1988.) Statisticians and toxicologists suggested the evaluation criteria of the dose response pattern of ABS. Margolin et al (1986) suggested to use Cochran-Armitage trend test (CA). Sofuni et al (1990) considered the dose response to be (strong) positive if it had two significant doses out of three dose groups and decided it to be weakly positive if it had only one significant dose and there was a significant trend. Galloway et al’s criterion for a positive response was a clear dose related increase in the cells with structural aberrations in one experiment or a reproducible single positive dose (Galloway et al, 1994). We will first formulate the above three procedures in terms of Cochran-Armitage trend test and the Dunnett type test and then compare the performance of these three procedures in terms of Monte Carlo simulation study. Then we will develop a software program from the chosen procedure for the toxicologist’s easy use of a statistical procedure.