Using ctDNA Methylation to Monitor Metastatic Colorectal Cancer Treatment (PROMET)

This study is testing whether measuring methylation patterns in circulating tumor DNA (cancer DNA found in the bloodstream) can help doctors better track how well treatment is working in patients with metastatic or recurrent colorectal cancer. **You may be eligible if...** - You are 18 or older - You have been confirmed by biopsy to have recurrent or metastatic colorectal cancer - You are eligible to receive radiation therapy combined with standard chemotherapy, with or without immunotherapy (PD-1 inhibitors) - You are expected to survive at least 6 months - You (or your legal representative) are willing to sign an informed consent form **You may NOT be eligible if...** - You received a blood transfusion during surgery or within 2 weeks before the study - You are pregnant or breastfeeding without using adequate contraception - You have a history of other cancers - Your condition or treatment plan does not meet the study's requirements Talk to your doctor to see if this trial is right for you.