Patterns and preoperative risk factors of occult lymph node metastasis in clinical stage I lung cancer.

Objectives: To investigate the patterns and preoperative risk factors of occult lymph node metastasis (OLNM) in patients with stage I lung cancer.

Methods: This retrospective study evaluated patients with clinical stage I lung cancer who underwent systematic lymph node dissection. OLNM frequency by lobe (upper/lower) and preoperative risk factors of OLNM were analyzed.

Results: Overall, 1512 patients (892 and 620 patients with upper and lower lobe cancers, respectively) were included. The rates of OLNM and skip metastasis were 11.2 % and 1.9 %, respectively. For N1 lymph nodes, the most common site of metastasis was the lobar lymph nodes (7.6 %), regardless of the cancer location, followed by the interlobar (2.9 %) and hilar (1.9 %) lymph nodes. For N2 lymph nodes, upper lobe cancers tended to metastasize to the superior mediastinum (4.2 % vs. 1.4 %, inferior mediastinum), while lower lobe cancers metastasized to the inferior mediastinum (5.0 % vs. 0.5 %, superior mediastinum). Smoking (hazard ration [HR]: 1.722, 95 % confidence interval [CI]: 1.206-2.460), non-peripheral location (HR: 2.374, 95 % CI: 1.663-3.389), maximal tumor size > 2 cm (HR: 2.335, 95 % CI: 1.488-3.663), consolidation/tumor (C/T) ratio > 0.75 (HR: 16.958, 95 % CI: 7.839-36.687), and pleural abutting (HR: 1.696, 95 % CI: 1.177-2.444) increased the risk of OLNM.

Conclusion: In stage I lung cancer, the most common site of metastasis is the lobar lymph nodes, regardless of tumor location. Therefore, when segmentectomy is performed, dissection of the lobar lymph node dissection is important for the intraoperative evaluation of lymph node metastasis. A C/T ratio > 0.75 is the strongest preoperative risk factor of OLNM.