The concept of borderline epithelial lesions of the breast remains a controversial one, both at the conceptual and practical levels. The work of Page and collaborators (17–20) has suggested the existence of a continuum between hyperplasia and carcinoma in situ, and that the risk for the development of invasive carcinoma correlates with the degree of proliferation and atypia. A small survey made among a group of five experienced surgical pathologists to test the degree of interobserver variability in this field indicates that this variability remains unacceptably high. Unfortunately, none of the special techniques that have been employed to date in an attempt to achieve a sharper and more reproducible separation between the various groups has yet fulfilled this goal.
Since an element of subjectivity in the microscopic interpretation persists and is unlikely to be completely eliminated, and in view of the fact that the current terminology suggests a sharper division than what the evidence seems to indicate, consideration could be given to adopt a terminology such as mammary intraepithelial neoplasia (MIN) of either ductal or lobular types, followed by a grading system.