CEACAM5 and squamous cell carcinoma: According to the National Academy of Clinical Biochemistry Guidelines for the use of Tumor Markers in Lung Cancer, recommended markers are Cyfra21‐1 and CEA before therapy and Cyfra21‐1 and/or CEA in post‐therapy follow‐up in patients with adenocarcinoma, squamous cell carcinoma, and large cell carcinoma.