Papillary lesions of the breast

Papillary lesions include benign and malignant lesions. As this array of papillary lesions cannot be differentiated by clinical and imaging means, the diagnosis relies on pathologic examination. Intraductal papillomas are benign, and often complicated by superimposed epithelial metaplasia or hyperplasia. When they are involved by atypical duct hyperplasia, the prevailing practice is to upgrade the diagnosis to ductal carcinoma in situ when the extent of involvement is ≥3 mm. Intraductal papillary carcinomas has low grade malignant epithelial changes, retaining an outer myoepithelial layer but lost the myoepithelial cells within the lesion around fibrovascular cores. Encapsulated papillary carcinomas and solid papillary carcinomas have distinctive morphology, but both are characterized by frequent loss of myoepithelial cells surrounding the lesion, although the current classification still consider these to be in situ lesions. Invasion is used for irregular groups, tongues and nests of tumor cells extending into the stroma beyond the rounded boundary. Immunohistochemistry is useful in differentiating papillary lesions, with positivity of myoepithelial markers, high molecular weight cytokeratins and heterogeneous staining of ER denoting benignity and vice versa. Core needle biopsy is frequently used in diagnosing papillary lesions: both under- and over-diagnoses may occur, the former being more frequent. Genetically papillary carcinomas are grouped mostly into luminal cancers, further attesting to the generally low grade nature of all subtypes of papillary carcinomas.