Consequently, the use of immunohistochemistry (IHC) based biomarkers such as Ki-67 together with HER2 status has been proposed to distinguish ER-positive breast cancer cases at high risk of disease progression (i.e., bona fide Luminal B tumors) from those at low risk of disease progression (i.e., bona fide Luminal A tumors) (7). Here, MKI67 is linked to breast cancer.