Accuracy of 18F-FDG PET/CT and factors contributing to unexpected pathologic lymph nodes in early-stage small cell lung cancer

Identifying metastatic mediastinal lymph nodes (LNs) using preoperative staging tools is essential for selecting appropriate surgical candidates among patients with small cell lung cancer (SCLC). Although fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) is currently regarded as the most reliable method, there remains a paucity of research on its accuracy in SCLC diagnosis. In this study, we evaluated the accuracy of 18F-FDG PET/CT and investigated the factors contributing to unexpected pathological LNs in SCLC cases with ambiguous N2 node involvement. A total of 34 patients diagnosed with early stage SCLC between January 2018 and July 2021 were included in the study. This retrospective analysis was designed to evaluate the diagnostic accuracy of 18F-FDG PET/CT compared to that of CT among various staging modalities. The sensitivity, specificity, and accuracy of 18F-FDG PET/CT were 45.5 %, 91.3 %, and 68.4 %, respectively. In comparison, CT demonstrated a sensitivity of 27.2 %, a specificity of 87.0 %, and an accuracy of 57.1 %. Multivariate analysis of both 18F-FDG PET/CT and chest CT identified tumor sizes >2.2 cm as the only independent and significant risk factor for nodal upstaging. Nodal evaluation for clinical staging using 18F-FDG PET/CT and chest CT in small cell lung cancer (SCLC) remains limited in guiding surgical candidacy. When N1 node involvement is inconclusive on 18F-FDG PET/CT, a biopsy may be recommended to confirm the SCLC stage using techniques such as endobronchial ultrasound or mediastinoscopy.