We then included these four variables in multifactorial COX regression analysis, revealing that high ECOG scores (HR=1.95; 95% CI: 1.23-3.10; P=0.005), more distant metastatic organs before treatment (HR=1.90; 95% CI: 1.12-3.23; P=0.017), and elevated plasma IL-6 levels (HR=2.83; 95% CI: 1.77-4.52; P<0.001) independently predicted poorer PFS in ESCC patients (Table 3, Figure 5C). This evidence concerns the gene IL6 and esophageal squamous cell carcinoma.