DKK1 and esophageal squamous cell carcinoma: In the assessment of the correlations of biomarker assays with clinical variables in ESCC patients in the training cohort and the validation cohort, DKK‐1, DKK‐1 autoantibodies or their combination showed almost no significant differences in positivity when the ESCC samples were subdivided by patient age, gender, size of tumor, site of tumor, depth of tumor invasion, histological grade, lymph node status, TNM stage or early‐stage and late‐stage groups (Tables S2, S3, and S4).