ERBB2 and breast cancer: Female patients aged between 25 and 75 years old who were newly diagnosed with HER2 positive breast cancer and scheduled to receive doxorubicin followed by trastuzumab adjuvant therapy, with Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2, preserved left ventricular (LV) systolic function in which the left ventricular ejection fraction (LVEF) ≥ 50%,normal hematological, renal function and Alanine amino transferase (ALT) ≤ 3 times upper limit of normal (ULN) were included in the study.