Effect of Gut Microbiota and Its Metabolites on the Efficacy of Immunotherapy in Metastatic Colorectal Cancer

This study is examining how gut bacteria (microbiota) and their chemical byproducts affect how well immunotherapy works in people with metastatic colorectal cancer. It is an observational study collecting stool and blood samples to understand these relationships. **You may be eligible if...** - You have been clinically and pathologically diagnosed with metastatic colorectal cancer - You are between 35 and 75 years old - Your medical records are complete - You have signed informed consent **You may NOT be eligible if...** - You have severe respiratory or heart disease - You have another type of cancer - You have severe active bleeding, uncontrolled infection, or an active stomach ulcer - You have moderate to severe kidney failure - The investigator considers you otherwise unsuitable Talk to your doctor to see if this trial is right for you.