Inhibition of azo dye carcinogenesis by thorotrast and iron oxide.

Evidence that the reticulo-endothelial system (R.E.S.) may be involved in the carcinogenic proc ess has been presented by Stern and Willheim (22) and by Jaffe (11). This system has also been im plicated in the metabolism of certain fat-soluble materials such as Vitamin A (3,10,17) and choles terol (3, 23) and the water-soluble vitamin, riboflavin (2, 9, 10). Since riboflavin is a factor in the carcinogenic!ty of the azo dyes (5, 6, 20) and since the lipide-soluble azo dyes may be taken up by the reticulo-endothelial cells of the liver (Kupffer cells), it was of interest to determine the effect of altered R.E.S. activity upon the incidence of liver tumors produced by carcinogenic azo dyes. Kinosito has reported that R.E. blockade "retards" the