In the present study, the highest diagnostic efficiency was achieved when a CAC counts of 3 was chosen as the cut-off value, this result is similar to the study conducted by Qiu [25] and Ye [18] et al. Overall, CAC counts presented better diagnostic value than commonly used tumour markers (CEA, CYFRA21–1, and NSE), which agrees with the results of several studies reporting the advantages of CACs for the diagnosis of lung cancer [17, 18, 24, 25, 27], CACs have the potential to become a better novel diagnostic marker of lung cancer. Here, CEACAM5 is linked to lung cancer.