The two agents showed consistent strong synergistic interactions against HER‐2‐overexpressing established human breast cancer cell lines, with drug concentrations used between 0.039 and 5.0 Amol/L for lapatinib and 0.31 and 4.0 Ag/mL for trastuzumab.5 Another mechanism was found that Lapatinib‐induced accumulation of HER2 and trastuzumab‐mediated downregulation of HER2 triggered enhanced immune‐mediated trastuzumab‐dependent cytotoxicity in SKBR3 and MCF7‐HER2 cells.6 Here, ERBB2 is linked to breast carcinoma.