ERBB2 and breast cancer: Future targeted therapeutic strategies for HER2 low-expression breast cancer will focus on the following improvements to the ADC class of drugs: (1) Modifying linker drugs and linker structures to maximise bystander effects; (2) Increasing the load of anti-personnel drugs; (3) Introducing double or even multiple resistances, etc. It is believed that the development of the ADC class of drugs for HER2 low-expression breast cancer will bring revolutionary advances in the diagnosis and treatment of this type of breast cancer.