In our daily practice of non-small cell lung cancer (NSCLC) surgery, we sometimes encounter cases of pathological stage was up because of unexpected lymph node metastasis. If single-station N2 metastasis without N1 (skip-N2) of the tumor ≤ 5cm was noted postoperatively, it becomes stage IIIA like other N2 disease, and is to be poor prognosis in the current TNM staging system. The aim of this study is to analyze the impact for prognosis and clinicopathologic characteristics of skip-N2 disease. We identified 415 patients with <T3 N1-2 NSCLC who underwent anatomical lung resection completely between January 2000 and December 2018. The degree of lymph node metastasis was classified into three; N1, skip-N2 and the other N2 (N2). The prognosis and clinicopathologic characteristics of patients were analyzed comparing skip-N2 with N1 and N2. The median follow-up time was 45.7 months. Cases with N1 was 215 (51.8%), skip-N2 was 48 (11.6%) and N2 was 152 (36.6%). Among 48 cases of skip-N2, only 8 cases (16.7%) was diagnosed as N2 preoperatively. 5-year overall survival rate (5y-OS) for N1, Skip-N2 and N2 were 70.9%, 65.7% and 45.3% respectively. 5-year recurrence free survival rate (5y-RFS) for N1, Skip-N2 and N2 were 69.8%, 60.4% and 36.0% respectively. Prognosis of Skip-N2 had similar N1 (5y-OS; p=0.476, 5y-RFS; p=0.534) and had a tendency of better prognosis than N2 (5y-OS; p=0.08, 5y-RFS; p=0.01). As for clinicopathologic characteristics (patients characteristics, tumor marker, tumor size, tumor location, clinical stage and pathological characteristics), there were no significant differences between Skip-N2 disease and the other N1-2 disease. In skip-N2, 98% of cases were found within the extent of lobe specific lymph-node dissection. From clinicopathologic factors which can be obtained preoperatively, it is difficult to predict skip-N2. But the possibility of skip N2 among clinical N0 is not high, almost of skip N2 were detectable during surgery; lobe specific lymph node dissection is appropriate for clinical N0. The prognosis of skip N2 showed similar outcome of N1 rather than N2, but the prognosis is not enough; adjuvant chemotherapy is necessary for this population.
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