The four subtypes of BC are: (I) luminal A (HR+/HER2−/low Ki-67), (II) luminal B (HR+/HER2−/high Ki-67) or (HR+/HER2+/any Ki-67), (III) non-luminal HER2+ (HR-/HER2 overexpression), and (IV) triple-negative (HR−/HER2−) along with the basal-like subtype [3,4]. This evidence concerns the gene MKI67 and breast cancer.