Lobe-Specific Lymph Node Dissection In Stage Ia Non-Small-Cell Lung Cancer: A Retrospective Cohort Study

OBJECTIVES: To investigate lymph node (LN) metastasis according to tumour location and assess the impact of lobe-specific LN dissection on survival in stage IA non-small-cell lung cancer (NSCLC).METHODS: We retrospectively analysed the data of patients with clinical stage IA NSCLC treated with lobectomy and systematic LN dissection at Asan Medical Center (Seoul, Korea) between June 2005 and April 2017. Patients who received neoadjuvant therapy had multiple primary tumours or missed the follow-up during the first postoperative year were excluded. The patients were divided into five groups according to involved lung lobes: right upper lobe (RUL), right middle lobe (RML), right lower lobe (RLL), left upper lobe (LUL) and left lower lobe (LLL), which were further divided into subgroups according to LN station metastasis. Overall survival (OS) and the incidence of metastasis were calculated for each subgroup. Efficacy indices (Els) were calculated to determine the correlation between each lung lobe and LN station, and the impact of the dissection of these stations on survival.RESULTS: A total of 1202 patients were analysed. The 5-year OS in the RUL, RML, RLL, LUL and LLL groups was 74%, 88%, 78%, 80% and 75%, respectively. The incidence of single LN station metastasis was 11%, 10%, 10%, 16% and 14%, respectively. The lobe-specific LNs for RUL, RML, RLL, LUL and LLL were stations 2/3/4, 4/7, 2/4/7, 4/5/6 and 6/7/9, respectively. Moreover, the LN stations with high Els for RUL, RML, RLL, LUL and LLL were 4, 7, 7, 5 and 7, respectively. In the RUL group, the incidence of metastasis to stations 2, 3 and 4 was 2.3%, 0.5% and 7.6%, and the El was 0.8, 0.3 and 4.3, respectively. In RML, the incidence of metastasis to stations 4 and 7 was 4% and 6%, and the El was 1.3 and 2.4, respectively. In RLL, the incidence of metastasis to stations 2, 4 and 7 was 4.4%, 5.6% and 8.3%, and the El was 1.3, 1.4 and 3.3, respectively. In LUL, the incidence of metastasis to stations 4, 5 and 6 was 1.4%, 11.8% and 2.5%, and the El was 0.4, 7.1 and 0.5, respectively. In LLL, the incidence of metastasis to stations 6, 7 and 9 was 1.1%, 5.7% and 1.7%, and the El was 0.6, 2.3 and 0.5, respectively. Furthermore, the OS of patients with lobe-specific LN metastasis was statistically significantly different from that of the non-lobe-specific LN metastasis group with P-values of <0.001 for RUL, 0.002 for RML, 0.002 for RLL, 0.001 for LUL and 0.003 for LLL.CONCLUSIONS: Our findings support the use of lobe-specific LN dissection in stage IA NSCLC. When LN stations with high El were negative, LN metastasis in other stations was unlikely. The incidence of LN metastasis beyond lobe-specific LN stations was similar to 1% in all subgroups. Dissection of non-lobe-specific LNs may not improve the OS; however, prospective randomized controlled trials are needed to modify the standard approach.