ERBB2 and breast carcinoma: Both Ab8 and trastuzumab exhibited specific binding to the human HER2 antigen in ELISA assays, as depicted in Figure 1B. Flow cytometry analysis showed that IgG Ab8 recognized HER2 expressed on the cell surface of HER2+ HCC1954 and BT474 breast cancer cell lines but did not bind to the HER2- MDA-MB-231 cell line (Figure 1C).