Since current conventional serum biomarkers such as carcinoembryonic antigen, cytokeratin 19 fragments 21-1, and neuron-specific enolase are unsatisfactory in both sensitivity and specificity of early detection of lung cancer, circRNAs, with a pooled sensitivity and specificity of 0.8 and 0.8, respectively, are relatively hopeful indicators so as to contribute positively to the improvement in the early diagnosis with lung cancer. Here, CEACAM5 is linked to lung cancer.