Abstract: In previous studies,low expression of human epidermal growth factor receptor 2(HER2) was considered ineffective against HER2-targeted therapy.After the announcement of the efficacy of new antibody conjugated drug,Detrastuzumab in the treatment of breast cancer with low expression of HER2,the diagnosis and treatment options of breast cancer patients with low expression of HER2 have become the focus of breast cancer experts.In order to standardize the clinical rational diagnosis and treatment of breast cancer with low expression of HER2,the Breast Oncology Group of Heilongjiang Medical Association,referring to the latest clinical research at home and abroad and the consensus of experts at home and abroad,formed the consensus of breast cancer with low expression of HER2 clinicopathological diagnosis experts after the discussion by the expert group in Heilongjiang province,to guide clinicians to make diagnosis and treatment decisions for breast cancer patients with low expression of HER2,so as to improve the survival and prognosis of patients.The consensus mainly includes the definition and interpretation of breast cancer with low expression of HER2,factors influencing the results of HER2 low expression,new detection methods,clinicopathological and molecular biological characteristics,and clinical diagnosis and treatment guidance for breast cancer patients with low expression of HER2,which systematically and comprehensively demonstrates the consensus of clinicopathological diagnosis and treatment for breast cancer with low expression of HER2.

Key words: Breast cancer, Low Human epidermal growth factor receptor 2 expression, Targeted therapy, Consensus