MKI67 and breast cancer: In order to get a deeper insight into the prognostic significance of PR, we retrospectively analyzed a cohort of 687 non-metastatic N0-1 luminal-like HER2 negative BC patients stratified into four subgroups based on PR and Ki67 expression levels as measured by IHC, with a cut-off of 20% according with the 2013 Saint Gallen International Breast Cancer Conference (4).