MKI67 and cancer: The immunohistochemical (IHC) subtypes based on the expression of the estrogen and progesterone receptor, the detection of overexpression of the human epidermal growth factor receptor 2 (HER2) oncogene, and Ki-67 labeling index, are routinely used to identify tumor subtypes with different clinical outcomes and responses to therapy, including Luminal A cancer, Luminal B cancer, HER2-positive cancer, and triple negative (TN) cancer (2).