Early Detection of Relapses in Stage IV Colorectal Cancer Patients

Inclusion Criteria: 1. Histological confirmed adenocarcinoma of the colon or rectum with synchronous metastatic disease (localized in liver or in liver and lung) eligible for surgery immediately or after neo-adjuvant treatment. 2. Planned primary treatment at one of the REDCLOUD participating hospital centers. 3. Evidence of at least one measurable lesion, as per RECIST 1.1. 4. Male or female ≥ 18 years of age at time of informed consent. 5. Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1. No prior chemotherapy neither for localized nor for metastatic disease. 6. No major comorbidities that would preclude the compliance with the planned therapeutic program as judged by the Investigator. 7. Life expectancy \> 3 months. 8. Availability of biological samples (blood and tumor tissue). 9. Patients enrolled in local prospective protocols, in which samples have been collected according REDCLOUD procedures may be included. 10. Signed and dated informed consent. Exclusion Criteria: 1. Any physical or medical condition that would contraindicate chemotherapy and/or surgery. 2. Any other metastatic site, except for liver and lung metastases 3. Transplant recipients 4. Known history of human immunodeficiency virus (HIV) infection. Note: HIV testing will only be conducted in jurisdictions specifically requiring it. 5. Known active hepatitis B or hepatitis C infection. 6. Pregnant or lactating women 7. Other co-existing malignancies or malignancies diagnosed within the last 5 years with the exception of localized basal and squamous cell carcinoma or cervical cancer in situ adequately treated