Successful Conversion Surgery after Zolbetuximab-Based Chemotherapy for Claudin 18.2-Positive Gastric Cancer with Peritoneal Dissemination and Cervical Lymph Node Metastasis: A Case Report

INTRODUCTION: Zolbetuximab, a monoclonal antibody targeting claudin (CLDN) 18.2, has been approved as a first-line treatment for patients with human epidermal growth factor receptor 2 (HER2)-negative and CLDN-positive advanced gastric cancer. Conversion surgery following chemotherapy has emerged as a promising strategy for improving outcomes in patients with stage IV gastric cancer. Herein, we report a case of CLDN-positive gastric cancer with peritoneal dissemination and cervical lymph node metastasis that was successfully treated with subtotal gastrectomy (sTG) following zolbetuximab-based chemotherapy. CASE PRESENTATION: A 73-year-old male was diagnosed with HER2-negative, CLDN-positive gastric cancer, accompanied by peritoneal dissemination and cervical lymph node metastasis. He received 6 cycles of zolbetuximab in combination with capecitabine and oxaliplatin as first-line chemotherapy. Primary tumor, peritoneal lesions, and lymph node metastases exhibited marked regression, including complete resolution of the metastatic cervical lymph nodes. Complete response was achieved according to the Response Evaluation Criteria for Solid Tumors. After confirming the disappearance of the peritoneal dissemination, the patient underwent sTG with D2 lymphadenectomy. Histopathological examination revealed a grade 2 therapeutic response and no residual lymph node metastasis. The postoperative course was uneventful, and the patient remained recurrence-free for 5 months after the conversion surgery. CONCLUSIONS: Zolbetuximab-based chemotherapy followed by conversion surgery is a promising therapeutic strategy for patients with CLDN-positive advanced gastric cancer.