CEACAM5 and squamous cell carcinoma: Depending on the histological classification of LC, it is possible to determine the following biomarkers: neuron specific enolase (NSE) and cancerous-embryonic antigen (CEA) in small cell LC; cytokeratin fragment (CYFRA 21-1), a marker of squamous cell cancer (SCC), and CEA in squamous cell cancer (13); СЕА, CYFRA 21–1 and СА-125 in adenocarcinomas, CYFRA 21-1, SCC and СЕА – in large-cell lung cancer (14, 15).