In situ proliferative epithelial lesions of the breast.

Considerable progress has been made over the last several years toward understanding the significance of noninvasive epithelial changes in the breast. This progress, in essence, is the result of categorizing in situ alterations according to their clinical significance, or more specifically, according to the risk that such lesions carry to the patient for development of a subsequent invasive carcinoma. This article summarizes the histopathological criteria that are currently used to define morphologic categories and, perhaps more importantly, it reviews the clinical implications of the diagnoses that result from this categorization.