ABSTRACT
Breast cancer has become the malignant tumor with the highest incidence rate among women, of which human epidermal growth factor receptor 2 (HER2) positive breast cancer accounts for about 15%-20%. With the development of anti HER2 targeted drugs, the survival and prognosis of HER2 positive breast cancer has significantly benefited. About 45%-55% of breast cancer patients have low HER2 expression, and these patients usually do not receive anti HER2 treatment. However, there is a significant difference between the biological behavior and prognosis of breast cancer with low HER2 expression and breast cancer with zero HER2 expression. It is helpful to differentiate and adopt corresponding treatment strategies to improve the prognosis of patients. At present, there have been many advances in targeted therapy of breast cancer with low HER2 expression, which provides a useful reference for precision treatment of breast cancer with low HER2 expression.