Hyperplastic alveolar nodules of the rat mammary gland: tumor-producing capability in vivo and in vitro.

Carcinogen-induced hyperplastic alveolar nodules failed to form tumors after transplantation into isologous female rats; instead they developed ductal or ductal-alveolar outgrowths. Mammary glands from mid-pregnant female rats showed similar outgrowths following transplantation to the isologous hosts. In vitro and in vivo studies failed to demonstrate that subcarcinogenic doses of 7,12-dimethylbenz(a)anthracene can induce mammary tumorigenesis in the hyperplastic alveolar nodules. Our observations suggest that carcinogen-induced hyperplastic alveolar nodules are not 'preneoplastic' lesions in mammary carcinogenesis in the rat.