Pathological Complete Response by S-1 Chemotherapy in Advanced Gastric Cancer

A pathological complete response (pCR) to treatment for gastric cancer is a rare event, even when powerful treatment regimens are used. Herein, a case of 61-year-old male referred to our hospital with advanced gastric cancer who achieved a pCR following chemotherapy using S-1, and subsequently underwent total gastrectomy is reported. His initial esophagogastroduodenoscopy (EGD) revealed an irregular, nodular, ulcerated lesion in the upper third of the stomach that was analyzed by biopsy to be a moderately differentiated adenocarcinoma. Abdominal contrast-enhanced computed tomography (CT) showed gastric wall thickening and lymph node swelling in the perigastric area. The patient was clinically diagnosed with cT3N1M0, stage IIB advanced gastric cancer. The patient decided against curative surgery due to his work circumstances and was started on S-1 (80 mg/m²) chemotherapy administered orally twice a day for 4 weeks, followed by 2 weeks of no chemotherapy. After four such courses of systemic S-1 chemotherapy, EGD showed a small, reddened lesion with aggregated, whitish lines. The gastric wall thickening and lymphadenopathy in the perigastric area were also reduced remarkably. The patient subsequently agreed to surgery, undergoing total gastrectomy with D2 lymphadenectomy. Gross examination of the surgically resected specimen showed a slightly erythrogenic, flat lesion measuring 1.5×1.0 cm. Pathological examination of the resected specimen and harvested lymph nodes detected no malignant cells. The postoperative course was uneventful. The patient has continued to receive S-1 chemotherapy, with no evidence of recurrence at 4 months post-surgery. To the best of our knowledge, this is only the second case of a gastric cancer patient achieving a pCR by S-1 monotherapy reported in the English literature and indicates the potential adoption of curative resection after S-1 chemotherapy as a treatment strategy for advanced gastric cancer.