In addition, Kaplan–Meier analysis of expression cohorts of ER+ breast tumors showed that high XIAP expression levels significantly (p < 0.0001) correlate with poor relapse-free survival [hazard ratio (HR) > 2] and poor distant metastasis-free survival (HR > 3) in tamoxifen-treated ER+ (luminal-A) breast cancer patients (Figure 2B). This evidence concerns the gene ESR1 and breast cancer.