A patient population with a histopathological diagnosis of moderate-grade intra-epithelial neoplasia (MGIN), high-grade intra-epithelial neoplasia (HGIN) and/or early flat-type SCCA of the esophagus, in lesions measuring 3 to 12cm in length, will be treated with radiofrequency ablation (RFA) using the HALO ablation system. Additional RFA sessions will be performed on 3 month intervals until complete response (CR; no MGIN or worse in biopsies) will be achieved. All patients will then undergo an endoscopy at 12 months after baseline. Patients with CR at 12 months will be followed-up for 5 years with annual endoscopy and biopsies, and additional treatment if necessary. Patients with no CR at 12 months are considered failures.