1. Voluntary participation in the study and provision of written informed consent.
2. Age ≥18 years at the time of signing informed consent.
3. Histologically confirmed colorectal adenocarcinoma with mismatch repair deficiency (dMMR) or microsatellite instability-high (MSI-H) status.
4. Clinically confirmed stage IV disease.
5. No prior immunotherapy for the current colorectal cancer.
6. Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.
7. Availability of adequate pretreatment tumor tissue and peripheral blood samples for whole-exome sequencing (WES) and personalized circulating tumor DNA (ctDNA)/MRD analysis.
8. Life expectancy \>12 months.
9. Willing and able to comply with the study procedures and scheduled follow-up.
You may not be if
1. Presence of another malignancy.
2. Prior immunotherapy for the current stage IV colorectal cancer.
3. Organ transplantation within 3 months before enrollment.
4. History of blood transfusion within 3 months before enrollment.
5. Active, known, or suspected autoimmune disease, or evidence of active or chronic infection with hepatitis B virus, hepatitis C virus, or human immunodeficiency virus (HIV).
6. Pregnancy or breastfeeding.
7. Presence of a serious concurrent disease that, in the investigator's judgment, may substantially affect life expectancy or study participation.
8. Failure to provide written informed consent.
9. Any other condition that, in the investigator's judgment, makes the participant unsuitable for enrollment.
