MKI67 and breast cancer: In 2013, BC was classified into luminal A BC (ER+, PR ≥ 20%, Her-2-, Ki-67 < 20%), luminal B BC (ER+, PR < 20% and/or Her-2+ and/or Ki-67 ≥ 20%, Her-2-overexpression (ER-, PR-, Her-2+), and basal-like (ER-, PR-, Her-2-) BC [6].