ERBB2 and breast cancer: Regarding the heterogeneous biological markers of breast cancer cell lines, we chose three representative subtypes: MCF-7 for luminal A subtype (ER+, PR+/−, HER2−), MDA-MB-468 for basal subtype (ER−, PR−, HER2−), and MDA-MB-231 for claudin-low subtype (ER−, PR−, HER2−), the latter two of which were also referred to as triple-negative cell lines (Holliday and Speirs, 2011).