Tumour markers, such as cytokeratin 19 fragment (CYFRA21-1), carcinoembryonic antigen, neuron-specific enolase (NSE), squamous cell carcinoma antigen, pro-gastrin-releasing peptide (proGRP), and cancer antigen 125, are currently used in clinical laboratories for the diagnosis and monitoring of lung cancer, but they are underutilised owing to their unsatisfactory diagnostic performance, particularly for lung cancer [11]. Here, CEACAM5 is linked to lung cancer.