Incidence of occult mediastinal node involvement in cN0 non-small-cell lung cancer patients after negative uptake of positron emission tomography/computer tomography scan.

OBJECTIVE: This study sought to assess the real incidence of pN2 among patients with non-small-cell lung cancer (NSCLC) (cN0) with negative mediastinal uptake of 2-deoxy-2-(18F)-fluoro-o-glucose (FDG).

METHODS: During 30 consecutive months (January 2007-May 2009), all patients with NSCLC scheduled for surgery in our unit had a preoperative FDG-positron emission tomography (PET)/computed tomography (CT) in our institution, after a dedicated chest CT (n=259). Only patients with both FDG-PET/CT and negative dedicated chest CT scan (N1 and N2 nodes <1cm) were prospectively included (n=125). Patients with cN1/cN2/cN3 and patients who had undergone preoperative chemo-radiotherapy were excluded. No invasive surgical staging was carried out in this group and curative resection plus systematic mediastinal dissection was performed except in the event of unexpected oncological contraindication. All variables were collected prospectively and, when pathological information was obtained, all the cases were carefully reviewed.

RESULTS: Mediastinal assessment by FDG-PET/CT, negative predictive value (NPV) was 85.6%, confidence interval (CI): [77-91]; false negatives (FNs) for mediastinal lymph nodes involvement was 14.4% (18 cases). The pN2 stations most frequently involved were: 4R (six cases), seven (six cases) and five (five cases). Multiple-level pN2 occurred in six (4.8%) cases. Occult (pN2) lymph nodes were more frequent in women (p<0.01), adenocarcinoma (p<0.05) and pN1 (p<0.05). Pathological N2 prevalence for pN1 was 34 (27.7%). Considering pathological staging as the gold standard, the agreement was 70% and 47.5% for stage IA and IB (Kappa's index: 0.72 and 0.76) and, in all patients, 47% (Kappa's index: 0.27). In general, down-staging is more frequent than up-staging.

CONCLUSIONS: Mediastinal staging of NSCLC by FDG-PET/CT showed a considerable incidence of FNs. NPV is lower than previously reported and the preoperative mediastinal staging by 18FDG-PET/CT may jeopardise the accurate treatment for early stage NSCLC patients.