Considerations on the preneoplastic lesions of the mammary gland.

The general characteristics of the preneoplastic lesions of the human mammary gland, as they are known through histologic description, are outlined, and data obtained from the experimental analysis of mammary gland preneoplasia in five areas of endeavor are discussed. Results obtained with transplantation procedures and aimed at defining the growth potential of hyperplastic outgrowths are reported. Information derived from the study of events able to induce benign hyperplastic outgrowths or their malignant transformation in the murine mammary gland is summarized. Attempts to predict neoplastic transformation in morphologically hyperplastic epithelium of human and rodent glands are discussed. The present status of efforts toward the prophylaxis of preneoplastic lesions of the mammary gland is described. Considerations of the relationship between preneoplasia and tumor dormancy conclude the presentation.