Impact of tumor location and pleural invasion on the frequency of skip hilar lymph node metastasis in lung cancer

Background: The appropriate extent of hilar lymph node (LN) dissection in segmentectomy for lung cancer has not yet been fully investigated. Herein, we assessed the patterns of LN metastasis using network analyses. Methods: Patients with nodal metastases of non-small-cell lung cancer measuring <= 30 mm in diameter who underwent anatomical resection were included. The assumed pathways of metastasis were visualized using Cytoscape software. Metastasis to hilar (#10) or interlobar (#11) LNs but not to more peripheral ones was defined as skip N1 metastasis. Results: A total of 322 patients were included, with 123 of them having pleural invasive tumors and 32 having intrapulmonary metastases. There were 130 patients with pN1 disease and 192 with pN2 disease. The overall proportion of patients with skip N1 metastasis was 17%. Patients with lower lobe tumors had more frequent skip N1 metastasis than those with upper lobe tumors (31% vs. 10%, P<0.001) but had less frequent skip N2 metastasis (10% vs. 20%, P=0.02). The rates of skip metastasis to #11i in the right S6 tumor and right S9-10 tumor were unexpectedly high (22% and 17%, respectively). Similarly, skip metastasis to #11 in the left S6 tumor was relatively high (16%). There was a significant difference in the frequency of skip LN metastasis between tumors with and without pleural invasion (44% vs. 27%, P=0.001). Conclusions: The pattern of LN metastasis differed according to the localized segment of the tumor and the pleural invasion status.