1. Five Sprague-Dawley strain rat groups were fed ad libitum a basal semi-synthetic diet containing 0.06 per cent 3′-methyl-4-dimethylaminoazobenzene (m′-Me-DAB). Four of these groups were simultaneously treated with 20-methylcholanthrene (MCA) by the following methods: dietary, peritoneal cavity implantation, subcutaneous implantation, and vaginal lavage.

  2. Rats on m′-Me-DAB lived no longer than 29 weeks, dying of tumor complications. Life was prolonged up to 40 weeks in rats receiving m′-Me-DAB and the polycyclic carcinogen simultaneously.

  3. Liver tumor development was either delayed or entirely inhibited by the simultaneous administration of the carcinogens m′-Me-DAB and MCA. Bile duct tumors were the type most inhibited.

  4. Cirrhosis of the liver was either delayed or entirely inhibited by the simultaneous administration of the carcinogens m′-Me-DAB and MCA.

  5. Metastases decreased in incidence. Adenocarcinoma of the liver-cell type was the only type involved in a local extension or confined to microscopic thrombi.

  6. The combined administration of MCA and m′-Me-DAB produced morphologic adrenal cortical change.

  7. In spite of liver tumor inhibition, lack of cirrhosis, and the adrenal cortical morphologic changes, MCA fibrosarcomas occurred in the animals receiving MCA subcutaneously and intraperitoneally.

*

This investigation has been aided by Cancer Teaching and Cancer Research Grants, National Cancer Institute, U.S. Public Health Service, The Damon Runyan Fund, and by the Oregon and Montana Divisions of the American Cancer Society.

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