MTOR and esophageal squamous cell carcinoma: The summarized estimates suggested that mTOR/p-mTOR expression was significantly correlated with the worse OS in patients with ESCC (HR: 2.04; 95 % CI: 1.58–2.62; P < 0.001; Table 4 and Fig. 3), without any heterogeneity (I2 = 0.0 %, p = 0.493).