Figure 1. The presentation of factors with influence on developing of Trastuzumab resistance. Despite improved results in breast cancer treatment with Trastuzumab, most patients with metastases experience disease progression due to primary or acquired resistance. In Trastuzumab-treated patients with locally advanced or metastatic HER2+ breast cancer, an objective response rate (ORR) of only 65% was observed [12]. The gene discussed is ERBB2; the disease is breast cancer.