CEA, as a glycoprotein involved in cell adhesion, varies significantly across histological lung cancer types, with the most elevated serum levels of CEA being associated with adenocarcinomas.30 CA 125 is another tumor marker produced by adenocarcinomas and useful in the differential diagnosis of adenocarcinomas.31 Table 4 illustrates the relationship of CEA and CA 125 levels with patient demographics and clinical characteristics in those with adenocarcinomas. The gene discussed is CEACAM5; the disease is lung cancer.