The management of non-small cell lung cancer (NSCLC) relies on the tumour–node–metastasis (TNM) stage, and the treatment regimen differs based on the N status. Positron emission tomography–computed tomography (PET–CT) has emerged as a powerful imaging tool for the detection of various cancers with a relatively low false-negative rate. We explored predictors to identify false-negative N2 disease in PET–CT.METHODS
A total of 284 consecutive cN0 patients with peripheral NSCLC who underwent PET–CT scans followed by curative intent resections were enrolled as a training set to identify predictors of occult N2 metastases by multivariable analysis. The accuracy and cut-off values for the predictors were calculated using a receiver operating characteristic curve. Clinical and pathological data were analysed retrospectively. An additional 151 patients were collected as a test set to validate the results, including the occult N2 rate and accuracy.RESULTS
In total, 8.5% (24/284) PET–CT-diagnosed N0 NSCLC cases had pathologically diagnosed N2 metastases. The SUVmax of the primary tumour was a unique independent risk factor for occult N2 NSCLC [P = 0.003, 95% confidence interval = 0.81–0.96, odds ratio (OR) = 0.88]. Occult N2 metastases occurred more frequently in the subcarinal (16/24) and right lower paratracheal lymph nodes (12/24). Accordingly, we divided the patients into two groups by SUVmax: the occult N2 rates in the SUVmax of <2.6 and SUVmax of ≥2.6 groups were 1.0% (1/100) and 12.5% (23/184), respectively (P = 0.001). In the test set, the occult N2 incidence rate was 9.3% (14/151), with the highest rates occurring in the subcarinal (9/14) and right lower paratracheal lymph nodes (6/14). In the two groups defined by SUVmax, the occult N2 rates were 4% (2/50) and 11.9% (12/101), respectively.CONCLUSIONS
The SUVmax of the primary tumour was an independent risk factor for occult N2 metastases in NSCLC patients diagnosed as clinical N0 by PET–CT. SUVmax of ≥2.6 of the primary tumour may indicate the risk of N2 metastases, and invasive mediastinal staging techniques or comprehensive therapy should not be ignored in these patients.