The World Health Organization (WHO) classification of tumors of the breast defines the international standards for tumor categorization and nomenclature. The fourth edition, published in 2012, provides an update on the current knowledge concerning the classification, immunohistology profile, differential diagnosis and genetics of these lesions. Compared to the previous edition, some terms have been modified, some entities were reclassified and some current molecular data have been added. This article focuses on invasive carcinomas. Definitions for histological diagnosis are supplemented by clinical, macroscopic and molecular characteristics as well as prognostic and predictive features.
