A 73-year-old man underwent distal gastrectomy, D2 lymphadenectomy, and Billroth Ⅰ reconstruction for Type 3 advanced cancer in the lower corpus lesser curvature in 20XX. After postoperative adjuvant chemotherapy, he self-detected a mass in the left breast. It was diagnosed as breast cancer. He underwent mastectomy and axillary lymphadenectomy 16 months after gastric cancer surgery. After postoperative adjuvant chemotherapy, gastric or breast cancer did not recur. However, periodic upper gastrointestinal endoscopy revealed an 8-mm 0-Ⅱa lesion in the anterior wall of the remnant middle stomach(Group 5)80 months after gastric cancer surgery. Endoscopic submucosal dissection(ESD)was performed, and radical resection was achieved. Periodic upper gastrointestinal endoscopy was performed thereafter; an ectopic 0-Ⅱa lesion was detected in the greater curvature of the remnant middle stomach(Group 5)21 months after ESD. Since this lesion suggested massive submucosal invasion, total resection of the remnant stomach and Roux-en-Y reconstruction were performed. The postoperative course has been favorable, and the patient has been alive without recurrence for 6 months postoperatively. A long period passes before intestinal juice reflux induces progression of a chronic inflammatory gastric mucosal lesion to cancer in the remnant stomach. Thus, long-term endoscopic follow-up may be necessary.