CEACAM5 and pulmonary emphysema: We selected the factors that differed significantly between benign and malignant pulmonary nodules, such as age, smoking, emphysema, diameter, spiculation (burr), vascular sign, and the serum levels of CYRFA21-1, CEA, miRNA-21-5p, and miR-574-5p to establish a prediction model for malignant nodules.