NDRG1 and breast cancer: Based on the meta-analysis of three studies, no correlation between NDRG1 protein expression and ER status was identified (P = 0.57, log OR: -0.49, 95% CI: -2.18-1.19, I2: 87.38%, 233 breast cancer with ER-positive/268 breast cancer with ER-negative, 3 studies, Fig. 6).