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The addition of radiotherapy to the S-1 plus oxaliplatin (SOX) chemotherapy regimen did not improve disease-free or overall survival in patients with pathologic T4 and\/or node-positive gastric adenocarcinoma who underwent D2 gastrectomy (ie, R0 resection with D2 lymphadenectomy), based on a phase III trial published by Wang et al in JAMA Network Open<\/a>.<\/p>\n \u201cThe primary findings therefore support chemotherapy alone after D2 gastrectomy as an appropriate adjuvant approach for most patients with T4 [and\/or] node-positive gastric cancer,\u201d the investigators wrote.<\/p>\n Study Details<\/p>\n The open-label trial focused on 620 patients aged 18 to 70 years with T4 (44.2%) and\/or node-positive (95.2%) disease and no evidence of metastasis who underwent D2 gastrectomy at five tertiary hospitals in China. They were randomly assigned in a 1:1 ratio to receive adjuvant SOX with radiotherapy (n = 309) or SOX alone (n = 311).<\/p>\n Patients assigned to the experimental arm received one induction cycle of SOX, followed by radiotherapy to 50.4 Gy in 28 fractions with concurrent S-1, and then three additional cycles of SOX. Those assigned to the control arm received six cycles of SOX every 3 weeks.<\/p>\n The primary endpoint was 3-year disease-free survival, with overall survival and adverse events assessed as secondary endpoints.<\/p>\n Key Findings<\/p>\n At the prespecified primary analysis, disease-free survival did not appear to differ between the arms (hazard ratio [HR] = 0.98, 95% confidence interval [CI] = 0.73\u20131.33). Kaplan-Meier estimates showed 3-year disease-free survival rates of 70.5% with SOX plus radiotherapy and 69.3% with SOX alone (log-rank P = .93).<\/p>\n Overall survival was also not found to differ between groups (HR = 0.86, 95% CI = 0.60\u20131.23). Estimated 3-year overall survival rates were 80.8% with SOX plus radiotherapy and 78.4% with SOX alone (log-rank P = .41).<\/p>\n Longer-term follow-up likewise showed no evidence of benefit from adding radiotherapy. At 5 years, disease-free survival rates were 60.0% with SOX plus radiotherapy and 57.3% with SOX alone (log-rank P = .76), and overall survival rates were 73.7% and 71.4%, respectively (log-rank P = .55).<\/p>\n Overall, subgroup analyses for disease-free survival did not appear to indicate differences in treatment effect across baseline subgroups. For overall survival, patients with T4a disease had a HR of 0.65 (95% CI = 0.43\u20130.98), although the interaction test did not demonstrate heterogeneity of treatment effect by T stage (P for interaction = .11).<\/p>\n Treatment-related adverse events were reported to be similar between the arms.<\/p>\n \u201cThese findings suggest that routine intensification with postoperative radiotherapy added to adjuvant SOX may not be warranted after D2 R0 resection for T4 [and\/or] node-positive gastric cancer,\u201d the investigators concluded. \u201cAny apparent overall survival difference in the T4a subgroup should be interpreted cautiously as hypothesis-generating and confirmed in future studies.\u201d<\/p>\n