Definition of precancerous and high-risk mammary lesions.

Intraepithelial (noninvasive) neoplasia of breast, the most potent precursor of invasive carcinoma, comprises two types: lobular carcinoma in situ and ductal carcinoma in situ. Their respective morphologic character, biologic significance and natural history are discussed. Borderline lesions, such as atypical lobular hyperplasia and atypical ductal hyperplasia, are defined and their importance as risk factors for subsequent carcinoma is emphasized. Analysis of the concept of fibrocystic disease recognizes a lack of both pathologic specificity and predictive value as a risk factor for malignant disease. Rather than referring to fibrocystic disease, this complex should be stratified in specific histologic types to understand better its biologic significance.