NDRG1 and breast cancer: Based on the meta-analysis of three studies, no correlation between NDRG1 protein expression and tumor grading was identified (P = 0.10, log OR: 0.84, 95% CI: 0.16–1.84, I2: 57.22%, 338 breast cancer with tumor grade III/132 breast cancer with tumor grade I + II, 3 studies, Fig. 3).