The anti‐tumor effect of endocrine therapy can only be achieved when the breast cancer is hormone receptor positive.[18] To investigate whether POU4F1 knockout‐induced functional ERα re‐expression might resensitize BLBC cell lines to anti‐estrogen therapy, we treated the breast cancer cell lines with tamoxifen, an antagonist of ERα. The gene discussed is ESR1; the disease is breast carcinoma.