Prognostic Significance of Regional/Systemic Metabolic Parameters on (18)F-FDG PET in Pulmonary Lymphoepithelioma-Like Carcinoma

BACKGROUND: Pulmonary lymphoepithelioma-like carcinoma (LELC) is a rare subtype of lung cancer with less than 700 cases being reported in the literature, and no specialized treatment guidelines have been established. The prognostic significance of metabolic parameters on (18)F-FDG PET in pulmonary LELC still remains unknown. METHODS: From July 2011 to September 2020, 76 pulmonary LELC patients undergoing pre-treatment (18)F-FDG PET imaging were enrolled, and PET parameters including maximum standard uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) were calculated. In addition, whole-body tumor burdens were categorized into primary tumor lesion (PRL), thoracic lymph-node lesion (TRLN), and distant metastasis (DM) for respective metabolic parameters acquisition. ROC curves were generated to evaluate the predictive performance of the PET parameters, and correlations between tumor burdens of the different regional lesions were analyzed using linear correlation analysis. The prognostic significance for progression-free survival (PFS) and overall survival (OS) was assessed using univariate and multivariate survival analyses. RESULTS: Tumor stage, pre-/post-treatment serum EBV-DNA copies, SUVmax (cutoff 17.5), MTV, and TLG were significantly associated with PFS and OS in univariate analysis. MTV and TLG (AUC = 0.862 and 0.857, respectively) showed significantly higher predictive value than SUVmax (AUC = 0.754) and remained independent prognostic indicators for PFS in multivariate analysis (P = 0.026 and 0.019, respectively). Besides, non-colinearity was detected between metabolic burdens of the different regional lesions. MTV(-PRL), MTV(-DM,) TLG(-PRL), and TLG(-DM) were identified to be independent prognostic factors for PFS and OS, whereas MTV(-TRLN) and TLG(-TRLN) were not. CONCLUSION: The study demonstrated that MTV and TLG had independent prognostic significance for pulmonary LELC, which supported the incorporation of (18)F-FDG PET imaging into clinical treatment protocols for pulmonary LELC and implied multi-disciplinary cooperation for primary and distant metastatic lesions to further improve prognosis.