Patients found pulmonary nodules by CT screening by will be enrolled in this study prospectively. Plasma cfDNA sequencing of these patients will be used to diagnose and monitor benign and malignant pulmonary nodules.

This study prospectively included patients with pulmonary nodules (0.5-3 cm) diagnosed by CT. Methylation of plasma cfDNA in these patients will be performed. Evaluation of benign and malignant diagnostic efficacy of cfDNA methylation in pulmonary nodules with definite pathological findings. Pulmonary nodules that temporarily not require invasive examination will be performed CT follow-up and dynamically monitored methylation changes of cfDNA. And the methylation changes were to establish a model for the diagnosis and monitor of benign and malignant pulmonary nodules.

Inclusion Criteria:

• 1. Inclusion criteria:

  1. Aged 40-80;
  2. Lung nodules were detected by CT (≥5mm，≤3cm);
  3. Patients fully understand the informed consent and can sign the informed consent in person.

Exclusion Criteria:

• 2. Exclusion criteria:

  1. Patients diagnosed with malignant tumors in the past;
  2. This image suggests pulmonary nodules with hilar or mediastinal lymph node enlargement；
  3. Pulmonary nodules are suspected of intrapulmonary metastasis of lung cancer or other malignancies；
  4. Past diseases or conditions that affect plasma cfDNA content, such as rheumatoid immunity and diseases of the blood system.
  5. The researchers concluded that there were other conditions that made it inappropriate to participate in this study

The population of this study are those who meet the inclusion and exclusion criteria.