A 70-year-old man with anemia was admitted to our hospital. A barium meal examination and upper gastrointestinal endoscopy revealed type III advanced gastric cancer in the antrum. Biopsy specimens from the tumor demonstrated a moderately differentiated adenocarcinoma. Laboratory examinations revealed a high level of serum tumor markers, including carbohydrate antigen (CA) 19–9 (578.5 U/mL). A computed tomography (CT) scan showed regional lymph node metastases; however, distant metastases and direct invasion to the surrounding tissues were not observed. The patient underwent curative distal gastrectomy with D2 lymphadenectomy. Resected specimens demonstrated a flat, elevated, type 5 advanced gastric. tumor that was 6.0 cm in diameter, located in the greater curvature of the antrum. The proximal margin of the resected specimen was free of residual cancer cells (85 mm). The pathological findings of the resected primary gastric carcinoma, expressed according to the Japanese Classification of Gastric Carcinoma, were moderately differentiated adenocarcinoma, mp, INFb, intermediate, ly1, v0. Additionally, 5 of the 29 resected regional lymph nodes were positive in only the No. 6 (subpyloric) region according to the Japanese Classification of Gastric Carcinoma. The pathological stage was classified as IIB based on the American Joint Committee on Cancer TNM staging classification for carcinoma of the stomach (7th edition, 2012). The patient’ postoperative course was uneventful; his high preoperative CA19–9 level normalized (26.3 U/ml), and he was discharged. Postoperatively, the patient underwent adjuvant chemotherapy with S-1 (100 mg/day). However, his carcinoembryonic antigen (CEA) levels ranged from 5 to 6 U/mL, and his CA 19–9 levels ranged from 40 to 120 U/mL beginning at six months after surgery. We monitored the patient via CT scans every 6 months and observed no evidence of recurrence. His tumor markers remained in that same range for several months, and therefore adjuvant chemotherapy with S-1 was continued. However, two years and two months after surgery, his CEA (12.7 U/mL) and CA 19–9 (714.0 U/mL) levels increased dramatically, and an 18F- fluorodeoxyglucose positron emission tomography (FDG-PET) scan was performed, which revealed an accumulation of FDG in the upper mediastinum but no other evidence of recurrence. Based on these results, a repeat CT scan was performed, which revealed an enlargement of a solitary superior mediastinal lymph node. The enlarged lymph node was suspected to be a metastatic lesion derived from the gastric cancer. The patient underwent tumor resection by right mini-thoracotomy two years and three months following the initial gastrectomy. The metastasized lymph node exhibited strong adhesion to the right brachiocephalic vein; however, it was on the periphery of the superior vena cava and therefore could be excised with the right brachiocephalic vein. The patient’s postoperative course was uneventful, and he was discharged on postoperative day 17. The resected specimen was 1.5 cm in diameter, and histological examination demonstrated a moderately differentiated adenocarcinoma. Both the primary tumor and the mediastinal node exhibited partially positive immunohistochemical staining for CK7, positive immunohistochemical staining for CK20, and negative staining for Her2, indicating that it was a metastatic adenocarcinoma from the gastric cancer. While the patient received adjuvant chemotherapy with S-1 (100 mg/day) following the initial surgery and because he developed recurrence, he subsequently received adjuvant chemotherapy with docetaxel (40 mg/m2 on days 1, 8 and 15) in a 28-day cycle after the second operation. Unfortunately, he developed recurrences in the superior mediastinum and some right costa at six months after reoperation. Therefore, he received combination chemotherapy with irinotecan (60 mg/m2) and cisplatin (40 mg/m2) every two weeks; although he had not previously received this regimen, he developed multiple mediastinal and bone metastases and died 18 months after the second operation.