Prolonged antitumor effect of indomethacin on autochthonous intestinal tumors in rats.

Intestinal tumors were induced in randomly propagated Lobund Sprague-Dawley rats by dimethylhydrazine dihydrochloride and by methylazoxymethanol acetate. At 14, 63, and 77 days after exposure to a carcinogen, rats were fed, ad libitum, indomethacin in the drinking water (20 mg/liter) for 20 and 40 weeks. The development of intestinal tumors was prevented or retarded significantly compared to that of control animals. Among control rats at 20, 40, and 52 weeks, the numbers of tumors per rat were relatively constant, but the individual tumors were increased in size.