Mammary gland as a morphological end point in carcinogenesis studies.

The murine mammary tumor system is characterized by the presence of intermediate preneoplastic mammary cell populations. The intermediate mammary cell populations are characterized as either alveolar hyperplasias or ductal hyperplasias. The most frequently encountered preneoplastic cell population is the hyperplastic alveolar nodule, which has been extensively characterized with respect to its biological and hormonal properties. While the alveolar hyperplasias are seen predominantly in mice infected with the mammary tumor virus, ductal hyperplasias are seen primarily in mice treated with chemical carcinogens. Both types of lesions can serve as morphological end points for carcinogenesis studies in the mammary gland.