To further assess the HER2-CD3-Fc bsAb-mediated HER2-specific antitumor effect, we generated the 4T1.2 (4T1) mouse mammary cancer cell line stably expressing the extracellular domain and transmembrane region of human HER2 (HER2-ECD, aa 1–675) (4T1-HER2-ECD) (Figure 5F) [55]. This evidence concerns the gene ERBB2 and breast cancer.