CXCR4 and lung adenocarcinoma: In this study, the aims were to: i) confirm whether expression of CXCR4 is associated with lymph node metastasis of lung adenocarcinoma in vivo; and ii) screen and identify circRNAs present in exosomes (exo-hsa_circRNA) that are associated with CXCR4 expression and have potential to serve as predictors of lymph node metastasis in lung adenocarcinoma.