Because locally far-advanced gastric cancer combined with adjacent tissue invasion has a poor prognosis, some phase 2 and 3 clinical trials of neoadjuvant chemotherapy (NAC) are performed in Japan. However, neoadjuvant chemoradiotherapy (NACRT) achieves superior local tumor control compared with NAC. This feasibility trial explored the feasibility and safety of neoadjuvant chemoradiotherapy (NACRT) in this type of gastric cancer.

Since S-1 (combined drug of tegafur, 5-chloro-2,4-dihydroxypyridine and potassium oxonate) was approved in Japan in 1999 after a large-scale clinical trial, adjuvant chemotherapy with S-1 has been the standard treatment for stage II/III gastric cancer. However, for far-advanced gastric cancer, various adjuvant chemotherapies, including S-1, have not achieved satisfactory results. Therefore, Japan Clinical Oncology Group (JCOG) is currently performing phase 2 and 3 clinical trials of neoadjuvant chemotherapy (NAC) for locally far-advanced gastric cancer. However, previous studies of NAC have reported a pathological response rate of 15-50% for the main lesion, indicating no significant effect on local tumor control.

On the other hand, other studies have reported that anticancer drugs, including S-1, have a radiosensitizing effect, and that neoadjuvant chemoradiotherapy (NACRT) achieves superior local tumor control compared with NAC. Therefore, we conducted a feasibility trial of NACRT with S-1 for locally far-advanced gastric cancer combined with adjacent tissue invasion.

Inclusion Criteria:

• Histologically proven gastric adenocarcinoma
• Tumor invasion of adjacent structures (T4) and/or tumors with bulky nodal metastases
• No metastases outside of Group 2 lymph nodes
• Neither peritoneal metastasis nor liver metastasis
• No other distant metastasis
• An Eastern cooperative oncology group performance status of between 0 and 2
• No prior radiation therapy
• Sufficient organ function

Exclusion Criteria:

• A synchronous or previously active malignancy
• Insufficient oral intake
• A history of severe allergy
• Watery diarrhea
• Severe co-morbidities
• Requiring therapy for pericardial effusion or pleural effusion
• Contraindications to S-1 or radiotherapy.

• Histologically proven gastric adenocarcinoma
• Tumor invasion of adjacent structures (T4) and/or tumors with bulky nodal metastases