General
Characterized by epithelial proliferation supported by fibrovascular cores +/- intervening myoepithelial cell layer
Carcinomas with predominantly papillary morphology have a better outcome
COMMON BENIGN FEATURES
Papillary lesion has a double cell layer (myoepithelial cells stain with p63 or calponin and are present in papillary fronds & periphery of involved space)
Epithelial cells have NO atypia- (NOTE: you can see ADH or DCIS in an IDP; Restricted luminal (pink) cytokeratin expression without brown myoepithelial cells supports the diagnosis of ADH)
Thick collagenous stroma within branching fibrovascular cores. Can have marked fibrosis (“sclerosing papilloma”). The overall appearance is heterogeneous with thick fibrovascular cores and other areas of adenosis.
Finding apocrine metaplasia is helpful (common in benign papillomas; unusual in papillary carcinomas)
ATYPICAL/MALIGNANT FEATURES
Increased cellularity surrounding the fibrovascular cores
Numerous epithelial cells not directly connected to a papilla (thin papillations)
Lack of myoepithelial cells
Fibrovascular cores can be very small and subtle (benign FV cores are thicker/more fibrotic)
Mitotic figures
Architectural complexity (Low power view may demonstrate circumscription and this within a dilated duct)
Papillary Breast Lesions: Common Diagnoses
Benign lesions:
Solitary (central) papilloma
Multiple (peripheral) intraductal papillomas
Atypical lesions:
Intraductal papilloma with ADH or DCIS
Malignant lesions:
Papillary DCIS
Encapsulated papillary carcinoma
Solid papillary carcinoma
Invasive papillary carcinoma