Circulating Tumor DNA Guided Therapeutic Strategies for CRC Patients With Small Pulmonary Nodules

Inclusion Criteria: 1. Age ≥ 18 and ≤80 years old, regardless of gender; 2. Pathologically confirmed as adenocarcinoma of advanced colorectal cancer; 3. Lung lesions only, which was considered as metastatic by imaging consultation, and clinically diagnosed as lung metastasis of colorectal cancer; 4. Multiple lung lesions are allowed, but the maximum lesion diameter should be less than or equal to 2 cm; 5. For lesions larger than 1 cm, local treatment is planned, such as radical surgical resection or local radiotherapy, radio frequency ablation or interventional therapy (absolute alcohol treatment or cryotherapy); 6. Eastern Cooperative Oncology Group (ECOG) score 1 \~ 2; 7. The subjects (or their legal representative / Guardian) must sign the informed consent form, indicating that they understand the purpose of the study, understand the necessary procedures of the study, and are willing to participate in the study; 8. Surgical specimens or puncture specimens containing tumor tissue are available; 9. 20 mL of peripheral blood are available (10 mL per tube, two tubes in total); 10. Agreed to follow up for at least 2 years. Exclusion Criteria: 1. The pathology was not confirmed by enteroscopic biopsy or biopsy of metastatic lesions; 2. Patients with stage I-III colorectal cancer; 3. Primary lung cancer, GGO, tuberculosis and other non metastatic conditions were excluded after diagnosis by imaging consultation; 4. Presence of metastasis other than lung; 5. Insufficient organ function, such as severe abnormal hemogram, abnormal liver and kidney function; 6. Any signs of severe or uncontrolled systemic diseases that the researcher believes may have a significant patient risk/benefit balance, including uncontrolled hypertension, severe infection, hepatitis B, hepatitis C and human immunodeficiency virus; 7. History of alcoholism or drug abuse; 8. Pregnant or lactating patients.