TTR and cancer: Various cancer biomarkers have been identified for lung cancer detection, including carcinoembryonic antigen (CEA) (28), cytokeratin fragment 21-1 (CYFRA21-1) (29), carbohydrate antigen 125 (CA125) (30), transthyretin (TTR) (31), haptoglobin (32), neuron-specific enolase (NSE) (33), GM2 activator protein (GM2AP) (34), carbohydrate antigen 19-9 (CA19-9) (35), p16 (36), and the KRAS (37).