Circulating Tumor Cells in Lung Cancer Screening

Inclusion Criteria: * Age 55 years or more * 30 or more pack-years of cigarette smoking history * Former smokers: quit smoking within the previous 15 years * Signed informed consent form * Presence of COPD * Affiliation to the French social security system Exclusion Criteria: * Chest CT examination in the 12 months prior to eligibility assessment(1) * Treatment for, or evidence of, any cancer other than skin basocellular carcinoma in the 5 years prior to eligibility assessment * Pneumonia or acute respiratory infection treated with antibiotics in the 12 weeks prior to eligibility assessment * Unexplained weight loss of more than 15 10%pounds in the 12 months prior to eligibility assessment * Recent hemoptysis * History of lung volume reduction with coils, glue or valves° * Metallic implants or devices in the chest or back, such as pacemakers or Harrington fixation rods * Participation in another cancer screening trial * Participation in a cancer prevention study, other than a smoking cessation study * Vulnerable persons: adults under guardianship, adults under trusteeship or persons deprived of their liberty, patients under 18 years old * Medical and/or psychiatric problems of sufficient severity to limit full compliance with the study or expose patients to undue risk 1. Many COPD patients will have had a previous chest CT examination. This has become common in medical practice, especially in patients with chronic lung diseases such as COPD patients. Including such patients would introduce huge bias in the study by artificially focusing on rapidly growing cancers. Redoing a CT in a screening intend in a patient who recently underwent this investigation would also unnecessarily enhance irradiation in these patients. It should be note that in the NLST trial "previous chest CT (≤ 18 months)" was a key exclusion criterion \[NLST Radiology 2011\].