The prognosis of breast cancer is closely associated with various clinicopathological characteristics, such as age, tumor size, pathological type, lymph node metastasis status, histological grade, lymphovascular invasion, Ki-67 index, hormone receptor (HR) status, human epidermal growth factor receptor-2 (HER-2) expression, etc. These well-known pathological features have been widely used to make clinical treatment plans and predict the prognosis of breast cancer. This evidence concerns the gene MKI67 and breast cancer.