Gallen International Breast Cancer Conference (2011) Expert Panel adopted the classification of five molecular subtypes of invasive breast cancer which have been differentiated using the immunohistochemistry (IHC)-based expression of estrogen receptor (ER), progesterone receptor (PgR), human epidermal growth factor receptor 2 (HER2), and Ki-672. This evidence concerns the gene ESR1 and invasive breast carcinoma.