Luminal-type (hormone receptor [HR]-, ER- or PR-positive) breast cancer is the most frequent type and is divided into luminal-A and luminal-B subtypes, which are defined by low- (Ki-67 < 14) and high- (HER2-positive or Ki-67 ≥14) proliferation subtypes [2,3,5]. The gene discussed is MKI67; the disease is breast cancer.