The Role of the Thyroid in Hydrocarbon-induced Mammary Carcinogenesis in Rats

The effects of surgical thyroidectomy and of exogenous thyroxin on the induction of mammary cancer with repeated doses of 3-methylcholanthrene (MCA) in Wistar female rats and with single doses of 7,12-dimethylbenz(a)anthracene (DMBA) in Sprague-Dawley female rats were minimal. These effects were evident only on the MCA-induction system: thyroxin subcutaneously inhibited tumor appearance slightly, and the inhibitory effects of thyroidectomy were attributable to reduced food intake. The DMBA-induction system was not affected by the procedures.