MKI67 and breast cancer: Accumulating epidemiological data suggest that breast cancer risk factors may be distinctly associated with grade and KI67.21, 22, 23 Three previous studies found associations between high BMI and high levels of histologic grade but not KI6721, 22, 23 whilst younger age at onset of breast cancer and being of African‐American ethnicity were reportedly associated with high levels of KI67 but not histologic grade.23 These studies were case‐series with limited sample sizes (346–668 cases), and were based on semi‐quantitative visual scores for KI67.