ESR1 and breast cancer: CSEA revealed the pathways characteristics of the integral genomic signature predicting Trastuzumab-based treatment responses in breast cancer patients, such as the MTORC1 signaling predicting sensitive response, a major downstream effector of HER2 signaling, and the ER and EMT pathways predicting resistant response, both of which are known to endow HER2 therapy and chemotherapy resistance in breast cancer.