We were interested in these five specific biomarkers since previous studies have suggested a correlation of histological tumour types with TMs: adenocarcinoma with CEA; squamous cell carcinoma with CYFRA 21-1 and SCC; large cell carcinoma with CYFRA 21-1 and NSE; and small cell lung cancer with NSE and ProGRP (Molina et al., 2010). Here, ENO2 is linked to adenocarcinoma.