Following the binding with the receptor, trastuzumab can disrupt the ligand-independent interaction of HER-2/HER3/PI3K complex downstream signaling, strengthen the activity of cell-cycle inhibitor p27 potentially, inhibit the growth of breast cancer, and cause the death of cancer cells by antibody-dependent immune cell-mediated cytotoxicity (67–69). The gene discussed is ERBB2; the disease is breast cancer.