Is Biopsy of Contralateral Hilar N3 Lymph Nodes With Negative PET-CT Scan Findings Necessary When Performing Endobronchial Ultrasound Staging?

Background: Systematic endobronchial ultrasound (EBUS)-guided lung cancer staging starts with hilar N3 nodes, proceeding sequentially to mediastinal N3, N2, and N1 nodes, with sampling of all enlarged nodes (size, ≥ 5 mm) by EBUS. However, procedure time is limited by patient comfort when moderate sedation is used. It is unclear if EBUS staging should start with hilar N3 nodes or whether starting with mediastinal N3 nodes suffices. Knowing the probability of hilar N3 nodes with PET-CT scan negative findings harboring occult metastasis can inform this decision. Research Question: What proportion of patients with hilar N3 nodes showing negative PET-CT scan findings have malignancy by EBUS? Study Design and Methods: This retrospective observational, single-center cohort study included consecutive patients with clinical-radiographic T1-3, N0-3, M0 non-small cell lung cancer undergoing systematic EBUS staging with biopsy of hilar N3 nodes with negative PET-CT scan findings. The primary outcome was the proportion of patients with malignant hilar N3 nodes showing negative PET-CT scan findings. Based on expert opinion, a threshold probability of malignancy of less than 5% was considered sufficient to skip hilar N3 nodes. We used the binomial exact test to compare the observed proportion vs threshold probability of 5%. Results: Of 1,737 consecutive patients undergoing EBUS staging, 1,567 showed negative PET-CT scan findings of the hilar N3 nodes. These nodes were enlarged by EBUS and were sampled in 739 patients. Malignancy was found in the hilar N3 nodes of 5 of 739 patients (0.68%; 95% CI, 0.22%-1.57%). The proportion was significantly less than the threshold probability (P <. 001). Patients with positive PET scan results of the mediastinal N3 nodes were at higher risk of having occult hilar N3 nodal metastasis (P =. 003), found in 3 of 46 patients (6.5%; 95% CI, 1.4%-17.9%) with positive PET scan results of the mediastinal N3 nodes. Interpretation: When using moderate sedation, because time is limited, it is reasonable to start with the mediastinal N3 nodes if the hilar and mediastinal N3 nodes show negative PET scan results. Patients with positive PET scan findings of the mediastinal N3 nodes probably should undergo hilar N3 node sampling.