Analysis of different HER-2 mutations in breast cancer progression and drug resistance

Studies over the last two decades have identified that amplified human epidermal growth factor receptor (HER-2; c-erbB-2, neu) and its overexpression have been frequently implicated in the carcinogenesis and prognosis in a variety of solid tumours, especially breast cancer. Lots of painstaking efforts were invested on the HER-2 targeted agents, and significantly improved outcome and prolonged the survival of patients. However, some patients classified as 'HER-2-positive' would be still resistant to the anti-HER-2 therapy. Various mechanisms of drug resistance have been illustrated and the alteration of HER-2 was considered as a crucial mechanism. However, systematic researches in regard to the HER-2 mutations and variants are still inadequate. Notably, the alterations of HER-2 play an important role in drug resistance, but also have a potential association with the cancer risk. In this review, we summarize the possible mutations and focus on HER-2 variants' role in breast cancer tumourigenesis. Additionally, the alteration of HER-2, as a potential mechanism of resistance to trastuzumab, is discussed here. We hope that HER-2 related activating mutations could potentially offer more therapeutic opportunities to a broader range of patients than previously classified as HER-2 overexpressed.