A bispecific antibody with one trastuzumab- and one pertuzumab-based Fab arm was constructed with “knobs-into-holes” based heterodimerization and post-expression assembly and could inhibit the proliferation of HER2-positive breast cancer cells; however, the anti-tumor activity of the bispecific construct was similar to the combination of trastuzumab and pertuzumab [23]. The gene discussed is ERBB2; the disease is breast cancer.