ERBB2 and breast cancer: Currently, the complications that arise from the use of HER2-targeted therapy in GC treatment are not fully understood, but the experience and information gained from HER2-targeted breast cancer therapy indicates that a large number of HER2-positive breast cancer patients are primarily resistant to anti-HER2 drugs, and almost all of the patients will have drug-resistant tumors following HER2-targeted therapy (66–69).