Early Detection of Head and Neck Superficial Squamous Cell Carcinoma in Patients With Esophagus Squamous Cell Carcinoma

the investigators randomly divide the eligible objects into two groups:1. objects in this group will first receive OE endoscopy observation and subsequent white light imaging(WLI) observation during oropharynx and hypopharynx; 2. objects in this group will first receive WLI observation and subsequent OE observation during oropharynx and hypopharynx. Then, the investigators will compare the detect rate of oropharyngeal and hypopharyngeal superficial squamous cell carcinoma of two groups to find if OE endoscopy can improve the detect rate of oropharyngeal and hypopharyngeal superficial squamous cell carcinoma in esophageal cancer patients.