Third, in the subgroup analysis according to the type of cancer, for ESCC patients, loss of KLF4 expression showed a trend of better prognosis though without statistical significance (HR = 0.83, 95% CI: 0.57–1.23, P = 0.355) which suggested that, similar to head and neck squamous cell carcinoma (HNSCC) [45], KLF4 might be a malignant transformation-related gene in ESCC, which still needs further investigation. This evidence concerns the gene KLF4 and esophageal squamous cell carcinoma.