A 76-year-old male underwent distal gastrectomy for gastric cancer and pathological findings showed Stage Ⅳ(T4a, N3a, M1, H0, P0, CY1)with HER2 positivity. He received chemotherapy with S-1 and oxaliplatin(SOX)plus trastuzumab and no disease progression was shown. However, because of Grade 3 adverse skin effects to S-1, he could not continue with the regimen. He switched to a regimen of ramucirumab plus paclitaxel, followed by nivolumab, and later irinotecan. However, the disease progressed and multiple lung metastases as well as a left adrenal metastasis appeared. Fifth-line chemotherapy with trastuzumab was administered. After 4 courses, the lung metastases reduced and the left adrenal metastasis shrank from 46 mm to 33 mm. These results were consistent with a partial response on the Response Evaluation Criteria in Solid Tumors. In addition, CEA and CA19-9 also decreased significantly. Unfortunately, after 10 courses, the patient's disease progressed.