The tumorigenicity of 5-azacytidine in the male Fischer rat

5-Azacytidine was administered to young adult male Fischer rats.Tumors were found in 31 out of 70 rats that had received 5-azacytidineand survived 18 months from the start of the experiment. Severalrats had multiple primary tumors. In the rats that were testedfor complete carcinogenicity a variety of tumor types was found.These included acute leukemia and malignant reticuloendotheliosis,and tumors of the testis, skin, and bronchus. No hepatic tumorswere found in the group that was tested for hepatic tumor initiation.Hepatocellular carcinomas were found only in the group thatwas examined for hepatic tumor promotion by receiving a priorinitiating dose of diethylnitrosamine. No tumors were foundin the age controls. Thus, in these initial experiments, 5-azacytidineappeared to be a complete carcinogen, inducing tumors in severalorgans, and a tumor promoter but not a complete carcinogen forthe liver.