NDRG1 and neoplasm: After the statistical model was changed in the meta-analysis, results showed a positive correlation between NDRG1 protein expression and tumor grading according to the fixed-effects model (P < 0.01, log OR: 0.87, 95% CI: 0.38–1.37, I2: 57.29%, 3 studies, Supplementary Fig. 1).