To overcome the false-positive rate and the radiation risk of lung cancer screening, such as conventional low-dose computed tomography (CT), various methods that rely on circulating tumor cell (CTCs), non-small cell lung cancer (NSCLC), and validated biomarkers including carcinoembryonic antigen (CEA), CYFRA 21-1, or neuron-specific enolase have been investigated for early lung cancer detection (Table 1 and Figure 4). Here, CEACAM5 is linked to neoplasm.