The main characteristics of HER2 negative include high expression of ER+/PR+, HER2– and Ki67, etc., while the main characteristics of HER2 positive include ER+/PR+, HER2+, etc. The main characteristics of HER2 overexpression type are HER2+, ER–/PR–, etc. When the expressions of ER, PR and HER2 are down-regulated, this breast cancer is called TNBC (De Abreu et al. 2013) and its percentage in breast cancer is 20%. This evidence concerns the gene MKI67 and breast cancer.