ERBB2 and breast carcinoma: The expression level of HER2 in CHO-K6 cells was detected significantly higher than that of breast cancer cell lines including SKBR-3, BT-474, MCF-7, and MDA-MB-231, as well as another clone of HER2-overexpressing CHO cell line HER2-K13 cells [35,36] (Figure 1A).