Occult nodal metastasis in patients with non-small cell lung cancer at clinical stage IA by PET/CT

Background and objective: The introduction of ¹⁸F-FDG PET/CT has enhanced the diagnostic accuracy of nodal staging for non-small cell lung cancer (NSCLC). We analysed risk factors for occult nodal metastasis in patients with clinical stage IA NSCLC as determined by ¹⁸F-FDG PET/CT. Methods: Data for 147 patients diagnosed as clinical stage IA NSCLC by PET/CT from 2005 to 2007 were retrospectively reviewed. All study patients underwent ¹⁸F-FDG PET/CT for lung cancer staging. They also underwent cervical mediastinoscopy or systematic lymph node dissection. Results: Cervical mediastinoscopy was performed in 78 patients (53.1%), and N2 involvement was detected in 3.8% (3/78) of these patients. Thoracotomy with systematic lymph node dissection was done in 144 patients. Four patients (2.8%, 4/144) were diagnosed with N2 disease after systematic lymph node dissection. Total N2 involvement was 4.8% (7/147). As 9.5% (14/147) of study patients had N1 disease, 14.3% (21/147) of patients had occult nodal (N1 or N2) metastasis. In univariate analyses, larger tumour size and a higher primary tumour maximum standardized uptake value >7.3 (SUV_max) were associated with occult nodal metastasis. Multivariate analysis demonstrated that a primary tumour SUV_max>7.3 was an independent predictor of occult nodal metastasis (odds ratio: 7.574; P=0.001). Conclusions: Preoperative PET/CT scans contribute to reduce the frequency of occult nodal metastasis compared with those reported in the pre-PET/CT era. The higher SUV_max in primary tumour was an independent predictor of occult nodal metastasis in patients with clinical stage IA NSCLC by PET/CT. The purpose of this study was to evaluate the prevalence and predictors of occult nodal metastasis in patients with clinical stage IA NSCLC by ¹⁸F-FDG PET/CT. Occult nodal (N1 or N2) metastasis were noticed in 14.3% of the study patients. A primary tumour SUV_max of >7.3 on ¹⁸F-FDG PET/CT independently predicted nodal metastases in this cohort of patients.