Carcinoembryonic antigen (CEA), a glycoprotein involved in the modulation of cellular processes, cell‐cell recognition and cell adhesion, is used worldwide as a biomarker in several malignancies.7 Data from a few studies have suggested that pretreatment CEA levels and changes from pretreatment levels during treatment are indicative of treatment response in lung cancer.8, 9, 10 However, these results were obtained from small cohorts of patients which differ largely e.g. in terms of stages of disease. Here, CEACAM5 is linked to lung cancer.