Papillary Breast Lesions: Diagnostic Challenges and Overview of Entities

Papillary breast lesions represent a morphologically and biologically diverse group of entities that include benign intraductal papillomas, papillomas with atypical ductal hyperplasia, with ductal or lobular carcinoma in situ, papillary ductal carcinoma in situ, encapsulated papillary carcinoma (with or without invasion), solid papillary carcinoma, and invasive papillary carcinoma. Accurate classification is often challenging particularly in core needle biopsies, and even in excision specimens can pose difficulties, especially for less experienced pathologists. This review summarizes the essential histological and immunohistochemical features of each lesion and highlights key diagnostic pitfalls and helpful clues in their differential diagnosis. While genetic testing is not routinely required for diagnostic purposes, recent studies have identified more or less distinct molecular alterations across the spectrum of papillary lesions. These findings may support future refinements in classification and understanding of these tumors.