During 250 months of following‐up, we found elevated expression of DNMT3B mRNA in BC was associated with unfavorable relapse‐free survival (RFS) in all BC patients (hazard ratio [HR] = 1.26, log‐rank p = 5.3×10−6, Figure 5A), especially in ERα‐positive BC (HR = 1.45, p = 1.5×10−6, Figure 5B). This evidence concerns the gene DNMT3B and breast cancer.