HER-2 positive breast cancer patients who live at high altitudes greater than 2000 meters for long periods of time and will receive trastuzumab-based targeted therapy will be enrolled. The subjects included early and advanced patients. Treatment regimens includes chemotherapy combined with trastuzumab, chemotherapy combined with trastuzumab and pertuzumab, trastuzumab alone, and trastuzumab plus pertuzumab. Electrocardiogram, cardiac ultrasound, NT-proBNP, and TNI will be tested every 3 months when the treatment begins. The primary endpoint is cardiotoxity. The second endpoints is pathologic complete response (pCR) rate in neoadjuvant therapy, objective remission rate (ORR) and disease control rate (DCR) in neoadjuvant and palliative therapy.
