[A new approach to predict carcinogenicity of chemicals quantitatively--ratio estimate method]

Based upon the results of battery of mutagenesis tests, a new approach, ratio estimate method (REM), for predicting carcinogenicity of chemicals quantitatively is described. If the tests are composed of n mutually independent experiments, a result's set is constituted:M = [M1,M2,..., Mn]. According to the formulas of probability, we have: P (C+/M)/P(C-/M) = [P(C+)/P(C-)]. (formula; see text) where P(C+/M)/P(C-/M) is the ratio of the probability of a carcinogen to a non-carcinogen with the result's set of M. P(C+) and P(C-) signify the probability of a carcinogen and a non-carcinogen. P(Mi/C+) and P(Mi/C-) represent the probability with which the result Mi can be obtained to a carcinogen or a non-carcinogen. Let (formula; see text) then beta = gamma/alpha. The value gamma can be derived from the sensitivity and specificity of mutagenesis tests. It is difficult to get the exact value of alpha but one can give its suitable range. For example, let a less than or equal to alpha less than or equal to b, then gamma/gamma + b less than or equal to P(C+/M less than or equal to gamma/gamma + a. Thus, the mean value P(C+/M) = gamma/2 (1/gamma + b + 1/gamma + a) could be taken as an estimated probability to predict the carcinogenicity. The application of REM to predict the carcinogenicity of a carcinogenic and a non-carcinogenic polycyclic aromatic hydrocarbon was illustrated. The error range of the value estimated by REM was also discussed in detail. The major advantage of REM is that it only demands to give an experiential range of P(C-)/P(C+) without pre-determining its exact value and the calculating process is simple and feasible to the toxicologists.