In addition, although serum levels of tumor markers such as carcinoembryonic antigen (CEA), fragments of cytokeratin‐19 (CYFRA21‐1), and neuron‐specific enolase (NSE) are commonly measured for the diagnosis of lung cancer, the results are often not very specific or reliable, with false‐positive results often occurring due to infections, benign tumors, pregnancy, or other factors.4 Here, CEACAM5 is linked to infection.