This study aims to investigate the utility of circulating tumor DNA (ctDNA) methylation sequencing in the diagnosis of primary lung cancer.

Plasma sample of patients with and without lung cancer will be collected and analyzed using methylation-sensitive enzyme sequencing method. Diagnostic performance of ctDNA methylation sequencing will be compared with that of tumor markers (CEA, Cyfra 21-1, and NSE) combined.

Inclusion Criteria:

• Lung cancer group

  1. Pathologically proven lung cancer
  2. Clinically suspected lung cancer on chest CT scan

• Benign pulmonary disease group

  • Chronic obstructive pulmonary disease, interstitial lung disease, pneumonia, bronchiectasis, non-tuberculous mycobacterial lung disease, pulmonary vascular disease

Exclusion Criteria:

• Patients with previous history of lung cancer
• Patients who have been diagnosed with other malignancy within 5 years
• Unstable vital status
• Active pulmonary tuberculosis
• Infection with hepatitis B virus (HBV), hepatitis C virus (HCV), or human immunodeficiency virus (HIV)

• Lung cancer

  1. Pathologically proven lung cancer

  2. Clinically suspected lung cancer on chest CT scan

     1. nodule, mass, pulmonary infiltrate, or consolidation
     2. size : diameter at least 1 cm
     3. CT attenuation of solid or part-solid
     4. planned to follow-up, biopsy, or surgical resection

• Benign pulmonary disease

  1. COPD : post bronchodilator FEV1/FVC < 0.7 and FEV1 pred < 80%
  2. ILD : either histologic or clinical diagnosis
  3. Pneumonia : community or hospital acquired
  4. Bronchiectasis : chest CT diagnosis
  5. NTM : at least 2 isolation of pathogen from sputum
  6. Pulmonary vascular disease : embolism, pulmonary hypertension, arteriovenous malformation