ESR1 and breast cancer: In addition, the mortality of patients with breast cancer was also related to Ki-67 expression level (χ2 = 7.889, P = 0.005), ER expression level (χ2 = 7.869, P = 0.005), PR expression level (χ2 = 17.917, P = 0.000), and pTNM stage (χ2 = 46.669, P = 0.000), as shown in Table 9.