Endoscopic radiofrequency ablation (RFA) is a rapidly evolving therapeutic modality, and recent studies have shown its efficacy and safety for eradicating for flat type early ESCNs. To search a best strategy for the prevention of ESCNs, the investigators thus propose a hypothesis that the preemptive RFA for esophageal "speckled" lugol background mucosa may prevent the metachronous neoplastic recurrence after complete endoscopic resection.