MKI67 and breast cancer: The resulting molecular subtypes are known as Luminal A (ER+ and/or PR+, HER2−, low Ki-67), Luminal B (ER+ and/or PR+, HER2− with high Ki-67 or HER2+ with any Ki-67 status), HER2-enriched (ER−, PR−, HER2+) and Triple-negative (TN) breast cancer (ER−, PR−, HER2−)6.