ERBB2 and cancer: To determine the overall similarities and differences of the three HER2 TKIs and other anti-cancer agents, we compared their IC50 fingerprints in the cancer cell line proliferation assays with those of 168 reference agents, including cytotoxic chemotherapies and many targeted inhibitors with diverse mechanisms of actions.16 The IC50 profiles of the three HER2 TKIs showed significant similarity with other TKIs and not with cytotoxic drugs, confirming the selective nature of the therapies (Fig. 2).