ERBB2 and cancer: To assess this hypothesis, we examined the efficacy of afatinib, an irreversible multitargeted tyrosine kinase inhibitor (TKI) of EGFR, HER2, and HER4 [11, 12], and we compared it to other drugs: lapatinib, which is also a TKI of EGFR and HER2 but weaker than afatinib in its EGFR inhibitory effect [12], and trastuzumab and pertuzumab, which have been demonstrated to be effective for treating cancers with wild-type HER2 amplification.