HIF1A and neoplasm: As shown in Table 2 and Additional file 2: Figure S1, HIF-1α expression did not show any significant association with gender (RR = 0.93, 95% CI 0.83–1.04, P = 0.179; fixed effects model: χ2 = 12.97, I2 = 7.5, P = 0.371), age (RR = 1.19, 95% CI 1.00–1.41, P = 0.055; fixed effects model: χ2 = 8.72, I2 = 42.7, P = 0.121), and tumor size (RR = 1.19, 95% CI 0.99–1.44, P = 0.069; fixed effects model: χ2 = 6.86, I2 = 12.6, P = 0.334).