CEACAM5 and lung cancer: Jiang et al. [21] (Jiang, Wang et al. 2018) investigated a combination of CEA, CYFRA21, NSE, and thymidine kinase 1 (TK1) for lung cancer diagnosis; the results showed that the diagnostic value of TK1 combined with CEA, CYFRA21-1, and NSE was significantly higher than that of each biomarker alone.