ESR1 and breast cancer: In univariate analysis, positive ER status of primary tumor (21.1% vs. 11.7%, p = 0.030), positive PR status of primary tumor (22.0% vs. 13.2%, p = 0.038), low Ki67 expression (34.9% vs. 13.6, p < 0.001), and the application of SLNB (31.0% vs. 15.5%, p = 0.023), showed association with the change of Ki67 expression between primary breast cancer and axillary LNM.