To further assess whether POU4F1 depletion in BLBC breast cancer cells confers tumor response to tamoxifen in vivo, we inoculated luciferase‐expressed wildtype MDA‐MB‐231 cells (WT) and POU4F1‐KO MDA‐MB‐231 into the mammary fatpads of female BALB/c nude mice, respectively, followed by subcutaneous embedding of tamoxifen or placebo pallets in mice (Figure 6C). This evidence concerns the gene POU4F1 and breast cancer.