HIF1A and neoplasm: However, high HIF-1α expression was related with tumor differentiation (RR = 1.56, 95% CI 1.00–2.43, P = 0.049; random effects model: χ2 = 28.33, I2 = 75.3, P <  0.001), clinical stage (RR = 1.75, 95% CI 1.25–2.45, P = 0.001; fixed effects model: χ2 = 8.89, I2 = 43.8, P = 0.113), and metastasis (RR = 1.78, 95% CI 1.58–2.00, P <  0.001; fixed effects model: χ2 = 24.91, I2 = 47.8, P = 0.024).