A Case of Unresectable Gastric Cancer Successfully Treated with Conversion Surgery After Immunotherapy Including...

Area of Science:

• Medical Oncology
• Gastroenterology
• Surgical Oncology

Background:

• Advanced gastric cancer with liver, pancreas invasion, and peritoneal dissemination presents a significant therapeutic challenge.
• Treatment guidelines for HER2-negative, MSI-high, and PD-L1-positive gastric cancer are evolving.
• Combination chemotherapy and immunotherapy are increasingly explored for unresectable gastrointestinal malignancies.

Observation:

• A 72-year-old woman with unresectable advanced gastric cancer received 11 cycles of S-1 and oxaliplatin (SOX) plus nivolumab.
• The patient's tumor exhibited HER2-negative, microsatellite instability-high, and PD-L1-positive characteristics.
• Post-treatment imaging revealed significant tumor reduction, decreased organ infiltration, and resolution of metastases.

Findings:

• Conversion surgery, including laparoscopic distal gastrectomy with D2 lymph node dissection, was successfully performed.
• Postoperative histopathology confirmed no residual tumor cells in the primary site or lymph nodes.
• The patient completed 1 year of adjuvant SOX therapy and remains alive and recurrence-free at 16 months post-surgery.

Implications:

• This case highlights the potential of neoadjuvant SOX plus nivolumab therapy for achieving downstaging and enabling curative-intent surgery in advanced gastric cancer.
• Complete pathological response after neoadjuvant treatment may predict favorable long-term outcomes in selected gastric cancer patients.
• Further research is warranted to evaluate the efficacy and safety of this combination regimen in a larger cohort of patients with similar tumor profiles.