Comparison of rat liver foci assay and strain A mouse lung tumor assay to detect carcinogens: a review.

A comparison was performed of the results reported in the literature of chemicals tested in the rat liver foci assay and/or in the strain A lung tumor assay to the results of the chemicals tested in long-term carcinogenicity bioassays. The rat liver foci assay was sensitive to 69% of 54 compounds found to be carcinogenic in long-term bioassays and the strain A lung tumor assay to 54% of 93 carcinogens. None of 10 compounds found to be noncarcinogenic in long-term bioassays were active in the rat liver foci assay, while 7 of 23 noncarcinogens (30%) were active in the lung tumor assay. Ten of the 17 carcinogens negative in the rat liver foci assay are believed to exhibit tumor-promoting activity; 3 are direct-acting alkylating agents (dimethylsulfate, epichlorohydrin, and beta-propiolactone); and the remaining 3 are azobenzene, 1,2-dibromoethane, and thioacetamide. Thirty-two of the 43 carcinogens negative in the lung tumor assay were active in either (1) the mouse liver only, (2) the rat and not in the mouse, or (3) in both the rat and mouse liver but not in other organs of the mouse. It is proposed that additional investigations be undertaken to further evaluate the rat liver foci assay and the strain A mouse lung tumor assay as short-term in vivo tests for the demonstration of the carcinogenic potential of genotoxic (mutagenic) chemicals and environmental samples of complex mixtures.