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The role of adjuvant radiation in locally advanced gastric cancer after a D2 lymph node dissection is not well defined. The Adjuvant Chemoradiation Therapy in Stomach Cancer trial demonstrated a benefit in selected patients with positive lymph nodes. This study further defines lymph node burden as a predictive factor for adjuvant radiation in locally advanced gastric cancer after radical D2 lymph node dissection.One hundred eighty-six patients with locally advanced gastric cancer and D2 dissections were retrospectively investigated. Patients were divided into 2 equal and well-balanced groups based on clinicopathologic characteristics, with half receiving chemoradiation and the other half chemotherapy alone. Clinical outcomes and recurrence patterns were compared. Lymph node ratio (LNR) was defined as ratio of positive to examined nodes. Chemotherapies were fluorouracil-based regimens. Radiation was prescribed to 45 Gy (range, 45 to 50.4 Gy) using 3-dimensional conformal or intensity-modulated radiation therapy techniques.There was no difference between patients treated with or without radiation in 3-year disease-free survival (DFS) (57.0% vs. 62.0%, P=0.30) or 3-year overall survival (72.8% vs. 77.4%, P=0.23). However, patients with LNR>0.65 or 3 to 6 positive nodes (N2) had improved 3-year DFS and 3-year distant metastasis-free survival (DMFS) in the chemoradiation group (LNR>0.65 vs. LNR≤0.65: 3-y DFS: 35.8% vs. 0%, P=0.052, 3-y DMFS: 75.2% vs. 0%, P=0.026; N2 vs. non-N2: 3-y DFS: 84.7% vs. 57.1%, P=0.046, 3-y DMFS: 100.0% vs. 65.3%, P=0.036).N2 or LNR>0.65 may be indications for adjuvant chemoradiotherapy. Further randomized studies are needed for validation.