Expression of tumor markers such as carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA19-9), carbohydrate antigen (CA125), cytokeratin 19 fragment (CYFRA21-1), and neuron-specific enolase (NSE) in serum have also been used to aid in cancer diagnoses, but these markers are not specific to lung cancer and may be associated with other pathologies6, 7. Here, CEACAM5 is linked to cancer.