Studies of the tumorigenic effect of two goitrogens.

The nature of tumors appearing in the thyroid gland and in the lungs of mice fed two standard goitrogenic drugs (MTU and MII) has been studied. These tumors have been considered malignant on the basis of their morphological appearance and their occurrence in abnormal locations. Some investigatiors, however, have questioned that they are actually malignant. The present results indicate that these tumors are most likely not malignant even if it is shown that the pulmonary nodules are of thyroid origin. The thyroid adenomas disappear once the goitrogen is withdrawn, but thryoid enlargement pesists, and event 6 months after discontinuation of the goitrogenic treatment , pulmonary nodules are still produced. Evidence is presented that these nodules are emoli from hyperplastic thyroid tissue and not tumors.