Biology of breast preneoplasia

The literature dealing with mammary cancer and the presence of the identifiable preneoplastic lesions in the mammary gland of several species has been reviewed. A discrete morphologically identifiable lesion with a high malignant potential is considered preneoplastic. Lobuloalveolar lesions have been identified in the human mammary gland which fit most of the criteria for preneoplasia. The lesions, hyperplastic atypical lobules, are multicentric, have a high statistical association with breast cancer and demonstrate a morphological progression through dysplasia to frank carcinoma. Other breast lesions have a high statistical association but no morphological progression can be seen and their neoplastic potential remains unknown. The significance of these correlations is enhanced by the occurrence of homologous breast lesions in outbred and inbred animal models. Statistical correlation with breast cancer and aberrant morphology has been accepted as presumptive evidence of preneoplasia in some animals. Definitive proof of the neoplastic potential has been obtained in rodent models by transplantation of the suspected lesions and their subsequent development into cancers. Although a strong morphological and statistical analogy exists between the human and animal models, the causes and biological potential of the human lesions await experimental proof.