ESR1 and breast cancer: Luminal breast cancers show high expression levels of several luminal epithelial cell markers like CK7, CK8, CK18 and CK19, MUC1, bcl-2, estrogen receptors (ER), progesterone receptors (PR), GATA3, epithelial cell adhesion molecules, and lower expression levels of basal CKs (CK5, CK14, and CK17).