To find out the roll of cellular oncogenes in 3'-methyl-4-dimethyl-aminoazobenzene (MeDAB)- induced carcinogenesis in rat, an experimental study was made using Sprague-Dawley rat. In additirm, to explore whether selenium could prevent the development of cancer in this model, selenium was also given. The resuits were as follow.. 1) Histnpathologic changes were proliferation of ovalocytes, proliferation of bile ducts, cholan- giodysplasia, and cholangiocarcinoma in sequence. 2) Induced carcinomas were all cholangiocarcinoma, but one case also showed the foci of hepatoceiluiar carcinoma and another one the foci of mixed tumor. 3) Selenium did not show the preventive effect on the development of cholangiocarcinoma induced by MeDAB. 4) One case with normal histology showed the elevated expression of 5 cellular oncogenes, namely H-ras. IC-ras, myc, fps, and myb. 5) Casec with cholangiodysplasia also showed the enhanced expression of cellular rmcogenes. 6) Four weeks after the cessation of the administration of MeDAB, 2 cases with the cholangiodys plasia did not show the elevated expression of any cellular oncogene, but 4 cases with cholangiocarcinoma showed the enhanced expression offps and/or myc, suggesting the important role of these two oncogenes in the final development of cholangiocarcinoma.
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