Keywords: esophageal cancer, prognostic biomarker, head and neck cancers, gastric cancer, the upper gastrointestinal tumors
INTRODUCTION
Esophageal cancer (EC) is the 7th most common tumor in the world (Global Burden of Disease Cancer Collaboration et al., 2018), ranking the 6th leading cause of cancer death, which seriously threatens human health (Bray et al., 2018). According to the data, it is estimated that 456,000 new cases of EC were reported worldwide in 2012, half of which were in China (Zhu et al., 2016).