Indications for invasive mediastinal staging in patients with early non-small cell lung cancer staged with PET-CT

Purpose/objective(s): Appropriate use of invasive mediastinal staging in patients with clinically node-negative NSCLC staged by PET-CT is critical in selecting patients for curative-intent therapy such as surgery or SBRT, but little data exists to guide this decision-making. We examined a large population of patients with clinical stage I NSCLC referred for mediastinoscopy or EBUS to find risk factors for occult N2 lymph nodes and determine which patients benefit from invasive staging.

Materials/methods: We identified consecutive clinical T1-2N0 NSCLC patients being evaluated for curative-intent therapy between 2011 and 2015. None had evidence of nodal disease by PET-CT; the endpoint was pathologic confirmation of occult N2 disease by EBUS or mediastinoscopy. Tumor size, location, histology, SUV_max, and radiographic appearance were evaluated as determinants of occult N2 disease. Two group comparisons of continuous variables were done with independent t-tests and categorical variables were compared with χ² or Fisher's exact test.

Results: In 284 patients with PET-CT-staged clinical T1-2N0 disease, the prevalence of occult N2 metastases was 7.0%. The negative predictive value of PET-CT was 92.9% and the negative predictive value of mediastinoscopy/EBUS was 96.3%. T2 tumors were more likely to have occult N2 disease than T1 tumors (11.8% v 3.6% p=0.009). Pure solid tumors had greater involvement of N2 nodes than tumors with any ground glass component (12.6% v 3.1%, p<0.001). 17.5% of central tumor cases were found to have occult N2 metastases while 4.4% of patients with peripheral tumors (P<0.001). 33.3% of patients with solid central T2 tumors had occult N2 metastases whereas 2.0% of patients with peripheral T2 tumors with a ground glass component, 1.2% of patients with peripheral T1 tumors with a ground glass component and 3.6% of patients with peripheral T1 solid tumors had N2 metastases.

Conclusions: Invasive mediastinal staging should be strongly encouraged in central tumors and solid T2 tumors because the risk of occult nodal involvement is greater than 10% in these cohorts. However, for patients with peripheral T1 tumors or peripheral T2 tumors with a significant ground glass component, the yield of invasive staging after a negative PET-CT is very low and invasive staging may not be warranted.