I. Introduction
Breast cancer is the second most common disease in females, and a primary leading cause of cancer deaths worldwide [1]. The severity of breast cancer can be divided into 5 stages (0-IV), which describes the extent of the breast cancer within patients' body [2]. The high mortality rate of breast cancer is mainly caused by initial diagnosis at the advanced stage. According to the statistics approved by Cancer. Net, most of breast cancer patients are diagnosed at the advanced stage, for which the 5-year survival rate is only about 26%. On the contrary, the 5-year survival rate of patients diagnosed at the early stage is up to 90%. Thus, the molecular mechanisms that intermediate longer survival time in breast cancer patients at the advanced stage are a hot spot in current research. However, the complexity of breast cancer and its significantly varied clinical outcomes now make it difficult to predict and treat [3]. Thus, being able to predict cancer prognosis more accurately not only assist breast cancer patients know about their life expectancy, but also assist physicians make informed decisions and further guide clinical therapy.