MKI67 and breast cancer: According to the morphological, molecular, and genetic heterogeneities,2 BC is divided into four major subtypes with the expression of markers (estrogen receptor, ER; progesterone receptor, PR; human epidermal growth factor receptor 2, HER2): luminal A (ER+ and/or PR+, HER2−, Ki‐67−), luminal B (ER+ and/or PR+, HER2+, Ki‐67+), HER2+ (ER− and PR−, HER2+), and basal or triple‐negative (ER−, PR− and HER2−).3