Risk-stratification models such as the IHC4 score [86,146,147,148,149] and the Magee equations TM [150,151,152,153], both use semi-quantitative information from the immunohistochemical assessment of Ki-67 and have been validated in retrospective studies as being able to identify patients at lower or higher risk of breast cancer relapse following endocrine therapy [148,149,150,151,152,153]. This evidence concerns the gene MKI67 and breast cancer.