Lymph Node Micrometastasis Prognosticates Survival for Patients with Stage 1 Bronchogenic Adenocarcinoma

Background This study aimed to investigate the significance of lymph node micrometastasis (LNMM) in the lung cancer nodal categories. Methods Between 1 January 2009 and 31 December 2013, 589 patients with suspected c-stage 1 and p-T1-2aN0-1M0 lung adenocarcinoma were enrolled in this study. The study evaluated LNMM with cytokeratin (AE1/AE3) and transcription factor-1 (TTF1) (8G7G3/1) expression by immunohistochemistry. Recurrence-free survival (RFS) and overall survival (OS) were compared among the T1-2aN0-1M0 patients stratified by the new N categories. Results From 589 patients, 7892 removed lymph nodes were examined, and LNMM was observed in 55 (9.3%) of the patients. The patients without LNMM or N1 had the best RFS (5-year rate: 80% vs 25%; P < 0.001) and OS (5-year rate: 87% vs 43%; P < 0.001), followed by the patients with LNMM, compared with those in the N1 category (RFS: 5-year rate, 25% vs 8%; P = 0.010; OS: 5-year rate, 43% vs 20%; P = 0.009). Similarly, this trend was observed when patients were subdivided into the T1 and T2a categories. Multivariate analysis showed that the new N categories with the addition of LNMM were an independent prognostic factor. This result also was noticed in all subgroups. Conclusions The findings showed LNMM to be clinically significant as a risk factor for lung cancer. Clinicians should consider LNMM when estimating N categories to determine prognosis and the best treatment strategy.