ERBB2 and cancer: One class belongs to the cytostatic effects through direct interaction with HER2 on cancer cells by the Fab (antigen-binding fragment) region of the antibody, such as suppression of HER2 downstream signaling [6,7], inhibition of HER2 extracellular domain shedding [8], blocking ligand-independent HER2/HER3 heterodimerization [9].