ERBB2 and cancer: The expression of P-gp/MDR1 gene in cancer stem cells was found to be related with the molecular subtypes of breast cancer tissue: basal-like subtype and normal-like subtype had both significantly higher P-gp expression than both Luminal subtypes and HER2 overexpressing subtype, while HER2-overexpressing subtype has shown a significantly higher P-gp/MDR1 expression than Luminal subtypes [51].