ERBB2 and breast cancer: Trastuzumab therapy may increase the risk of brain metastases in some patients with breast cancer.6, 7 Trastuzumab treatment costs approximately US$45 000 a year in China, which is an enormous financial burden to families of breast cancer patients.8 To overcome resistance and improve the efficacy of trastuzumab treatment in HER2‐overexpressing breast cancer patients, we must perform a thorough inquiry into the mechanisms of trastuzumab resistance and develop new effective treatment programmes.