Effects of Ovariectomy on Preneoplastic Nodule Formation and Maintenance in the Mammary Glands of Carcinogen-Treated Rats

In view of the known hormone-dependency of carcinogen-induced rat mammary tumors, the effect of ovariectomy on the initiation, formation, and maintenance of the preneoplastic lesion, the hyperplastic alveolar nodule, was studied. Initiation of mammary cell alterations in Lewis rats by 7,12-dimethylbenz[a]anthracene did not require concomitant action of ovarian hormones, although minimum prior exposure of the animal to these hormones may still be essential. The survival and maintenance of preneoplastic cells, whether in the form of nodule progenitors, hyperplastic nodules, or hyperactive nodule outgrowths, were not affected by ovariectomy. On the other hand, the hormonal milieu provided by the ovaries was necessary for multiplication of altered cells leading to nodule formation, as well as for outgrowth of nodules and tumor growth.