165 - Long-Term Prognostic Analysis of Chemoradiotherapy vs. Chemotherapy after D2 Resection for High-Risk Gastric Cancer: Results from a Prospective Randomized Control Study

X. Qiao¹, N. Li^1,2, Q. Hou³, Y. Tang⁴, J. Shi¹, and J. Jin^1,5; ¹State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College (PUMC), Beijing, China, ²Department of Radiation Oncology, Shanxi Province Cancer Hospital/ Shanxi Hospital Affiliated to Cancer Hospital, Chinese Academy of Medical Sciences/Cancer Hospital Affiliated to Shanxi Medical University, Taiyuan, China, ³Department of Radiobiology, Shanxi Province Cancer Hospital/ Shanxi Hospital Affiliated to Cancer Hospital, Chinese Academy of Medical Sciences/Cancer Hospital Affiliated to Shanxi Medical University, Taiyuan, China, ⁴Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, ⁵?Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China, Shenzhen, China

Purpose/Objective(s): To explore the prognosis value of postoperative chemoradiotherapy in patients with D2-resected, high-risk, node-positive gastric cancer. Materials/

Methods: This randomized clinical trial enrolled patients between October 1, 2011, and December 31, 2019. Patients with pathologically confirmed gastric cancer (stage anyT, N+, M0) who underwent D2 gastrectomy were randomized (1:1) to receive postoperative chemoradiotherapy (CRT) or adjuvant chemotherapy. The interventions of the adjuvant chemotherapy group were 8 cycles of SOX (S-1+Oxaliplatin) chemotherapy. The radiotherapy was given after 4-6 cycles of SOX chemotherapy. Radiotherapy (RT) comprised 45 Gy in 25 fractions of 1.8 Gy over 5 weeks by the intensity modulated radiation therapy (IMRT) technique concurrently with S-1 chemotherapy. The primary endpoint was 3-year disease-free survival (DFS). Acute toxic effects were assessed and graded according to the Common Terminology Criteria for Adverse Events version 4.0.
Results: The trial closed in June 2022 due to slow patient enrollment. A total of 308 patients (median [IQR] age, 58 [23-74] years; 221 [71.8%] men and 87 [28.8%] women) were enrolled, including 157 patients randomized to the adjuvant chemotherapy group and 151 patients to the adjuvant chemoradiotherapy group. One hundred and twenty-one (46.5%) patients had stage III disease. Three-year DFS was 67.2% for the control arm and 67.5% for the experimental arm (hazard ratio [HR], 1.08; 95% CI, 0.69-1.70; P =0.74). There was no significant difference between groups in overall survival (HR, 0.81; 95% CI, 0.49-1.33; P=0.40) or local recurrence (HR, 1.58; 95% CI, 0.66-3.82; P =0.31). After analyzing the number of positive lymph nodes and the location of lymph node metastasis in the patients, we defined pN staging=N2 patients with extra-perigastric lymph node metastasis as the high-risk group and the remaining patients as the low-risk group. The three-year DFS for the high-risk group and the low-risk group was 59.8% and 76.2%, respectively (HR, 2.05; 95% CI, 1.30-3.25; P<0.05). For high-risk patients, the three-year DFS in the adjuvant chemotherapy and adjuvant chemoradiotherapy group were 54.0% and 71.2%, respectively (P<0.05). More grade 3 and 4 acute toxic effects were observed in the adjuvant chemotherapy group than in the chemoradiotherapy group (42 patients [26.8%] vs 18 patients [17.5%]; P=0.08), but the difference was not significant.
Conclusion: The result of the subgroup analysis from the randomized clinical trial found that high-risk patients could benefit from the adjuvant chemoradiotherapy.