Breast cancer

Abstract

Breast cancer (BC) is a type of cancer originating from the epithelium of the mammary gland. As most cancers, it can be invasive or noninvasive. Carcinomas can originate from ducts (70 %) or from lobules (10 %). Rare subtypes (mucinous, tubular, medullar, cribriform, and adenoid cystic cancers) make up the rest. Besides histology, BC is classifi ed according to the expression of the estrogen receptor (ER), with 70 % being positive (ER +) and 30 % being negative (ER-), or the expression of the oncogene HER2 encoding the human epidermal growth factor receptor 2 (HER2), with 20–25 % Her2 + BCs and 75–80 % Her2-BCs. Today, a classifi cation by a combination of gene expression profi ling and classical pathology into four subtypes, luminal A, luminal B, Her2 overexpression, and basal-like BC, is commonly used (Table 1, adapted from [ 1 ]).