SLC39A6 and esophageal squamous cell carcinoma: Univariate Cox proportional hazard regression analysis revealed that lymph node metastasis [hazard ratio (HR) = 2.315, 95 % CI 1.226–4.371, P = 0.010], clinical stage (HR = 2.146, 95 % CI 1.134–4.063, P = 0.019), and SLC39A6 (HR = 2.780, 95 % CI 1.230–6.281, P = 0.014) were significant prognostic predictors for OS of ESCC patients in the entire population (Table 5).