ERBB2 and breast cancer: Luminal A subtypes of breast cancer are positive in the expression of estrogen (ER) and progesterone (PR) receptors and negative in the expression of HER2 (ER+/PR+/HER2–) and also shows the expression of Cytokeratin (CK) markers such as CK7, CK8, CK18 and CK19 [4, 5].