Background and purpose: Based on the 6th edition of the American Joint Commission on Cancer (AJCC) staging system for esophageal squamous cell carcinoma (ESCC), M1a node involvement was classified as regional node involvement in the revised 7th/8th edition. However, the clinical significance of M1a node involvement is unclear. Thus, we analyzed the prognostic value of M1a node involvement in patients with ESCC after definitive concurrent chemoradiotherapy (CCRT). Materials and methods: In total, 188 patients with ESCC had M0 disease according to the 7th/8th edition AJCC. We reclassified 31 (16.5%) of these patients as having M1a disease according to the 6th edition. After definitive CCRT, we compared baseline characteristics between the two groups and analyzed the rates of responders and recurrence. Finally, we compared prognoses according to overall survival (OS), disease-specific OS, and disease-free survival (DFS). Results: Among 31 patients reclassified to have M1a disease, 21 (67.7%) had supraclavicular lymph node metastasis and 10 (32.3%) had celiac lymph node metastasis. The number of responders was significantly lower for M1a disease based on univariate (p = 0.004) and multivariate (p = 0.011) analyses. Significantly lower survival rates were observed in individuals with M1a disease (median OS, 16.4 vs. 42.7 months; 5-year OS, 10.8% vs. 41.2%). Conclusions: M1a node involvement should be differentiated from regional node involvement.
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