Mammary hyperplastic and preneoplastic changes: taxonomy and grading.

Mammary lobular and ductal carcinoma in situ are thought to originate from preneoplastic precursors. Most of our knowledge on mammary tumorigenesis is based on experimental data obtained in rodents, which are focused on the biology of hyperplastic alveolar nodules (HAN). The morphology of HAN is analyzed and compared with possible analogous lesions in humans. The microarchitecture of the terminal duct lobular unit (TDLU) is described with reference to descriptions and nomenclature appearing in the literature. A comparison is intended between existing classifications of human hyperplastic and preneoplastic changes.