The investigators recruited consecutive patients with head and neck cancers, history of squamous esophageal cancers treated by chemoradiotherapy or endoscopic resection. Endoscopic surveillance first started with NBI for detection and characterization of early esophageal cancers through observation of abnormal intrapapillary capillary loops (IPCL). Superficial esophageal neoplasia were diagnosed by IPCL Type IV, V1,V2 and Vn. Lugol chromoendoscopy would be performed subsequently and suspicious neoplasia were classified as understain or unstain lesions. The diagnostic accuracy, sensitivity and specificity of NBI were compared to Lugol chromoendoscopy with histology serving as a gold standard.