ERBB2 and neoplasm: With regard to the influence of HER2 on sensitivity to EGFR-TKIs, Cappuzzo et al explained that the increasing cooperation between EGFR and HER2 led to better response to TKIs when the presence of increased copy number of HER2, while the high level of HER2 amplification made the tumor become more dependent on HER2 than EGFR signaling and therefore led to drug resistance [90].