Nodal staging in lung cancer: a risk stratification model for lymph nodes classified as negative by EBUS-TBNA.

Background: Over the last 10 years, endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) has become established as the first-line nodal staging procedure of choice for lung cancer patients. However, the pathway for patients following a negative EBUS-TBNA has not been clearly defined. The primary aim of this study was to develop and validate a risk stratification model to categorize lymph nodes deemed negative by EBUS-TBNA into "low-risk" and "high-risk" groups, where "risk" refers to the risk of false negative sampling.

Methods: A retrospective analysis of a prospectively maintained database at a UK tertiary EBUS-TBNA centre was performed. Only patients with primary lung cancer and only negative lymph nodes by EBUS-TBNA were included in the analysis. A risk stratification model was built from a derivation set using independent predictors of malignancy and the validation set used to evaluate the constructed model. The study period was from March 2010 to August 2013.

Results: Three hundred twenty-nine lymph nodes were included in the analysis (derivation set n = 196, validation set n = 133). Lymph node standardized uptake value, the standardized uptake value ratio between the lymph node and primary tumor, and heterogeneous echogenicity during sonographic assessment were the only independent predictors of malignancy. Using a simplified scoring system based on the natural logs of the odds ratios from the multivariable analysis on the derivation sample, lymph nodes can be stratified into low risk (score ≤1) and high risk (score ≥2). One hundred forty-one of 142 and 94 of 96 lymph nodes classified as low risk in the derivation and validation set, respectively, were ultimately proven to be benign and 35 of 54 and 24 of 37 lymph nodes classified as high risk were proven malignant. The negative predictive value of the risk stratification model for the derivation set and validation set was 99.3% (95% confidence interval 96.1%-99.6%) and 97.9% (95% confidence interval 92%-99.6%), respectively.

Conclusion: This risk stratification model may assist lung cancer multidisciplinary teams in deciding which patients need further staging procedures and which may proceed directly to treatment after a negative EBUS.