The significant variables for never smokers include age, gender, BMI, family history of lung cancer, AFP, MMEF, and CEA, the significant variables for light smokers include age, sex, smoking status, smoking pack-year, family history of lung cancer, AFP, and CEA, and the significant variables for heavy smokers include age, sex, smoking status, smoking intensity, BMI, MMEF, and CEA (Table 2). The gene discussed is CEACAM5; the disease is lung cancer.